Variable reflectance mirror system

ABSTRACT

Anisotropic film laminates for use in image-preserving reflectors such as rearview automotive mirror assemblies, and related methods of fabrication. A film may comprise an anisotropic layer such as a light-polarizing layer and other functional layers. The film having controlled water content is heated under omnidirectional pressure and vacuum to a temperature substantially equal to or above a lower limit of a glass-transition temperature range of the film so as to be laminated to a substrate. The laminated film is configured as part of a mirror structure so as to increase contrast of light produced by a light source positioned behind the mirror structure and transmitted through the mirror structure towards a viewer. The mirror structure is devoid of any extended distortion and is characterized by SW and LW values less than 3, more preferably less than 2, and most preferably less than 1.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/496,620 filed on Jul. 1, 2009 and now published as U.S.2009/0296190, which is a continuation-in-part of U.S. patent applicationSer. No. 12/191,804 filed on Aug. 14, 2008 and now issued as U.S. Pat.No. 7,679,809, which is a continuation of U.S. patent application Ser.No. 11/179,793 filed on Jul. 12, 2005 and now issued as U.S. Pat. No.7,502,156, which claims priority from U.S. Provisional Application No.60/587,113 filed on Jul. 12, 2004, U.S. patent application Ser. No.12/496,620 claims priority from U.S. Provisional Application Nos.61/079,668 filed on Jul. 10, 2008 and 61/093,608 filed on Sep. 2, 2008.The disclosure of each of the above-mentioned references is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to polymer-based film laminates and, moreparticularly, to automotive rearview mirrors incorporating laminatescomprising polymer-based film structures having an optically anisotropiclayer.

BACKGROUND ART

Mirror assemblies have proven to be a convenient location for providingdrivers with useful information. For example, a video display disposedbehind a mirror, but visible through a portion of the mirror, may supplythe driver with a video image of the scene to the rear of the vehiclewhere the driver's view may otherwise be obstructed. Similarly, aninformation display may offer the driver such vehicle-telemetryinformation as vehicle speed, engine status, oil level and temperature,for example, or any other information of interest. Integration of backupor other displays behind the automotive rearview mirror is generallypreferred over placing them adjacent to the mirror, thereby increasingthe area of the overall mirror assembly and impairing the driver's viewthrough the windshield.

Various types of displays incorporated within the rearview automotivemirror are known in the art, such as alphanumeric displays, graphicaldisplays, video displays, and combinations thereof. These displays arediscussed, for example, in U.S. Pat. No. 7,221,363, and in US PatentPublication No. 2008/0068520, each of which is incorporated herein inits entirety by reference. Displays that have been, or might be, used inautomotive applications employ various principles such as vacuumfluorescence (VF), electromechanics (EM), light emitting or organiclight emitting diodes (LED or OLED), plasma display panels (PDP),microelectromechanical systems (MEMS), electroluminescence (EL),projection (the projection systems include but are not limited to DLPand LCOS), or liquid crystal technology (used in liquid crystaldisplays, or LCDs), to name just a few. High-resolution LCDs capable ofdelivering color images, for example, may be mass-produced reliably andat low cost. LCDs are also noteworthy in that the liquid crystal mediumchanges its polarizing properties under the influence of the appliedelectric field and the light emanating from an LCD is polarized.

A particular challenge presented by display technology in an automotivecontext is that of providing the driver with sufficient luminance to seethe display clearly, especially under daunting conditions of ambientlight, while, at the same time, providing a clear and undistortedreflected view of the rear and peripheral scene to the driver. Sinceautomotive reflectors serve a crucial safety function in identifyingobjects otherwise outside of the driver's field of view, they mustcritically preserve image quality.

SUMMARY OF THE INVENTION

Embodiments of the invention provide an image-forming optical reflectorcomprising a base element (such as an electrochromic element or a prismelement) that reflects ambient light incident upon it, a light source,and a laminate that includes an anisotropic film disposed between thebase element and the light source. In one embodiment, the image-formingreflector may include a variable reflectance mirror system for use in arearview mirror assembly having a light source transmitting light of afirst polarization through the mirror system. The mirror system may be amulti-zone mirror system. The anisotropic film may extend across thefull field-of-view of the mirror system or, alternatively, it may extendsubstantially over only a transflective zone of the multi-zone systemthrough which the light source transmits light towards a viewer. Thefilm receives the light from the light source, transmitting a portion ofthis light that has a first polarization and reflecting a portion ofthis light that has a second polarization that is opposite to the firstpolarization. The mirror is substantially devoid of any extendeddistortion. In one embodiment, the mirror system is characterized bysurface values SW and LW, derived as discussed below, which do notexceed 3, preferably do not exceed 2 and most preferably do notexceed 1. The anisotropic film may be laminated between a substrate anda superstrate, which may be releasably adhered to the film. The lightsource may be a part of the laminate and may act as the superstrate.Alternatively or in addition, the base element may be a part of thelaminate and may act as the substrate. In a specific embodiment, thelaminate may be a stand-alone component of the reflector. The lightsource may comprise a display subassembly, for example an LCDsubassembly. In a specific embodiment, at least one of areflectance-enhancing and an opacifying layers may be additionallyemployed adjacent to a surface of the substrate and superstrate. Theopacifying layer may substantially cover a portion of the surface thatis located outside the transflective portion of the mirror structure.

Additional embodiments of the invention provide an optical element foroptimizing transmission of light through an image-forming opticalreflector. In a specific embodiment, the optical element of theinvention placed within the mirror system of the invention increases acontrast of light transmitted from a light source through the mirrorsystem to a viewer The optical element may comprise an opticalsubstrate, having a surface, and a light-transmitting layered structureadhered to the surface, where the layered structure includes ananisotropic layer that transmits light of a first polarization andreflects light of a second polarization that is opposite to the firstpolarization. The anisotropic layer may be birefringent. Layers of thelayered structure, including the anisotropic layer, may each haveassociated glass transition temperatures, and the layered structure maybe characterized by a range of glass transition temperatures. In oneembodiment, the layered structure is characterized by SW and LW that donot exceed 3 after the layered structure has been heated to soften atleast a portion of the plastic film, which generally occurs at atemperature approaching or exceeding at least a lower glass-transitiontemperature from the range of glass transition temperatures associatedwith the layered structure. In another embodiment, after having beenheated to such softening temperature under uniform (and, preferably,substantially omnidirectional) pressure, the layered structure issubstantially devoid of any extended distortion. In one embodiment, theoptical element may be a laminate integrating at least a substrate andthe anisotropic layer. In another embodiment, the optical element mayadditionally comprise a light-transmitting optical superstrate disposedover the layered structure where the optical superstrate may or may notbe releasably coupled to the layered structure. The optical element issubstantially devoid of any extended distortion and may be characterizedby values SW and LW that do not exceed 3, preferably do not exceed 2 andmost preferably do not exceed 1. In a specific embodiment, the opticalreflector may be an image-forming reflector, for example a rearviewautomotive mirror.

In accordance with another embodiment of the invention, a method isprovided for fabricating a laminate containing an APBF for use in arearview mirror assembly. The method includes disposing a film structurecharacterized by a predetermined water content and having a layer withanisotropic optical properties on a substrate to form a composite. Themethod further includes applying heat and pressure at controlledhumidity levels and, optionally, vacuum to the composite underconditions causing formation of a laminate that comprises a part of theimage-forming and image-preserving reflector characterized by SW and LWvalues that are less than 3, preferably less than 2, and most preferablyless than 1. According to one embodiment of the invention it ispreferred that the water content of the APBF prior to lamination be lessthan about 0.6 weight-%, more preferably less than about 0.4 weight-%,even more preferably less than 0.2 weight-%, and most preferably lessthan about 0.1 weight-%. The temperature selected to laminate thecomposite may be within a range from about 50° C. to about 160° C.,preferably between about 80° C. to about 150° C., and most preferablybetween about 90° C. to about 110° C. The pressure chosen for laminationis preferably substantially omnidirectional and may be between about 25psi to about 2,500 psi, preferably from about 50 psi to about 500 psi,and most preferably from about 100 psi to about 400 psi. The filmstructure may be optionally stretched during the lamination process toassure adequate flatness of the film. In one embodiment, the fabricatedlaminate may be additionally annealed to enhance the strength of thelamination bond. In one embodiment, the layer with anisotropicproperties transmits light having a first polarization and reflectslight having a second polarization that is opposite to the firstpolarization, and the laminate is characterized by SW and LW values lessthan 3, preferably less than 2, and most preferably less than 1. Inanother embodiment, the laminate is substantially devoid of any extendeddistortion and the optical reflector comprising such laminate forms animage satisfying automotive industry standards.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will be more readily understoodby reference to the following detailed description, taken with referenceto the accompanying, drawn not to scale, drawings where like featuresand elements are denoted by like numbers and labels, and in which:

FIG. 1 schematically illustrates an automotive rearview mirror assemblywith reduced optical quality resulting from a laminate that isfabricated conventionally and that is incorporated within the mirror.

FIG. 2 demonstrates an optical image formed in reflection from alaminate-containing display of a Nokia phone.

FIG. 3 is a flow-chart depicting steps of fabricating a laminate for usein an automotive rearview mirror assembly, in accordance with anembodiment of the invention. FIG. 3(A) illustrates an optionalpre-lamination treatment of a polymer-based film. FIG. 3(B) shows a stepof assembling a composite to be laminated. FIG. 3(C) illustrates a stepof lamination of the composite of FIG. 3(B). FIG. 3(D) depicts alaminate resulting from the lamination step of FIG. 3(C). FIG. 3(E)illustrates an optional step of releasing the superstrate of thelaminate, during or after the lamination procedure, resulting in analternative embodiment of the laminate as shown in FIG. 3(F). FIG. 3(G)schematically illustrates the steps of post-lamination processingincluding a step of inspection of the embodiments of FIGS. 3(D) and3(F), an optional step of post-lamination anneal, and an incorporationof an embodiment of a laminate into an automotive mirror assembly.

FIG. 4 schematically illustrates APBF-containing embodiments of rearviewmirror assemblies of the invention. FIG. 4(A): an APBF is laminated in arearview electrochromic mirror assembly. FIG. 4(B): an embodiment of theAPBF-laminate is incorporated, as a stand-alone component, into arearview tilt prism mirror assembly. FIGS. 4(C,D): an APBF is laminatedin a prism mirror assembly. FIG. 4(E): a display performs as a substrateof a laminate containing an APBF. FIGS. 4(F,G): an APBF-containinglaminate is integrated in a prism mirror structure containing a gap.FIG. 4(H): an APBF-containing laminate is integrated in a mirrorstructure containing a wedge-shaped gap. Light source is not shown inFIGS. 4(B-D, F-H).

FIG. 5 is a photograph of an electrochromic mirror assembly comprisingan embodiment of the laminate of the invention and forming an image of areference grid object positioned behind the viewer.

FIG. 6 presents a schematic cross-section of the embodiment of FIG. 5.

FIG. 7 shows auxiliary optional steps of the embodiment of the method ofthe invention illustrated in FIG. 3.

FIG. 8 shows reflecting structures pertaining to automotive rearviewmirror assemblies. FIG. 8(A) shows a prior art embodiment. FIG. 8(B)illustrates an embodiment of an APBF-containing laminate without asuperstrate. FIG. 8(C) illustrates an embodiment of an APBF-containinglaminate including a superstrate. FIGS. 8(D-G) show alternativeembodiments of lamination of an APBF between an EC-element and anadditional lite of glass. FIG. 8(H) demonstrates a perspective view ofanother embodiment of the invention. FIG. 8(I) shows another embodimentof the invention containing an APBF laminated between the EC-element andan additional lite of glass including a graded-thickness opacifyinglayer. FIG. 8(J) shows an embodiment similar to the embodiment of FIG.8(D) but including a stand-alone additional lite of glass with agraded-thickness opacifying layer disposed thereon.

FIG. 9 illustrates spectral dependences of reflectance characteristicsof embodiments of FIG. 8. FIG. 9(A) shows a reflectance curve for theembodiment of FIG. 8(B). FIG. 9(B) shows reflectance curves for theembodiments of FIGS. 8(B,C). FIG. 9(C) shows reflectance curves for theembodiments of FIGS. 8(C,D). FIG. 9(D) shows reflectance curves for theembodiments of FIGS. 8(D-G).

FIG. 10 graphically presents the date of Table 3.

FIG. 11 schematically illustrates the reflection and transmission ofambient light upon its interaction with an embodiment of the invention.

FIG. 12 shows the change in reflectance of the embodiment of FIG. 8(J)as a function of a position across the front surface of the embodiment.

FIG. 13 schematically illustrates embodiments used to enhance contrastof a display as perceived by a user wearing polarizing sunglasses. FIG.13(A): a light output from a conventionally oriented LCD is depolarized.FIG. 13(B): polarization of light output of a conventionally orientedLCD is rotated.

FIG. 14 depicts a photograph of a reference image formed according tothe visual evaluation test in reflection from another alternativeembodiment of the invention.

FIG. 15 illustrates experimentally measured results of the thermalanalysis of a DBEF-Q film, showing a glass transition temperatureregion.

FIG. 16 diagrammatically illustrates another APBF-laminate-containingmirror sample evaluated for extended distortions in the indicated areas.

FIG. 17 illustrates types of gradual edges in a chromium opacifyinglayer used with embodiments of the current invention. FIG. 17(A):Tapered gradient. FIG. 17(B): Feathered gradient. FIG. 17(C): Front viewof an opacifying layer with graded edges that limit the layer in ahorizontal direction. FIG. 17(D): Spatial distribution of thickness ofthe opacifying layer of FIG. 17(C).

FIG. 18 schematically illustrates, in side view, majorsubassembly-blocks of an automotive rearview mirror containing anelectronic device behind the mirror system.

FIG. 19 provides an example of the use of a reflective polarizercombined with a depolarizer in a display application.

FIG. 20 shows an alternative embodiment of the present invention.

FIG. 21 shows alternative embodiments of the present invention. FIG.21(A): a laminate including a PSA and having a superstrate removed. FIG.21(B): a laminate including a PSA and having both a substrate and asuperstrate.

FIG. 22 shows yet another alternative embodiment of the presentinvention.

FIG. 23 shows another embodiment of the present invention.

FIG. 24 shows an embodiment including an opaque reflectance-enhancinglayer.

FIG. 25 shows an embodiment containing two angularly misalignedreflective polarizers.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Definitions

As used in this description and the accompanying claims, the followingterms shall have the meanings indicated, unless the context requiresotherwise:

A “laminate” refers generally to a compound material fabricated throughthe union of two or more components, while a term “lamination” refers toa process of fabricating such a material. Within the meaning of the term“laminate,” the individual components may share a material composition,or not, and may undergo distinct forms of processing such as directionalstretching, embossing, or coating. Examples of laminates using differentmaterials include the application of a plastic film to a supportingmaterial such as glass, or sealing a plastic layer between twosupporting layers, where the supporting layers may include glass,plastic, or any other suitable material.

An “image-forming” or “image-preserving” reflector is a reflectorforming an essentially undistorted image in specularly reflected light.In imaging, optical distortion is understood as a deviation fromrectilinear projection. For example, an undistorted image of a straightline formed in a flat reflector is a straight line. For the purposes ofthis invention, “image-forming” and “image-preserving” includeprojections that may incorporate pre-determined distortions introducedby design into an otherwise undistorted image. For example, animage-forming reflector designed to be non-flat (such as a convex or anaspheric reflector) produces substantially no deviations from thecurvilinear image resulting from the design curvature of the reflector.

“Transflective” refers to an optical configuration that reflects atleast a portion of light incident from at least one side, and transmitsat least a portion of light incident from at least one side.

An “isolated defect” in an optical element is defined as a deformationfeature that may be surrounded with a complete annulus within whichthere is no excursion from the mean figure of the surface perceptible toan ordinary user. Such highly localized defects, moreover, arecharacterized by high spatial frequency when described in a Fourierdomain. For example, a particle of dust trapped within a laminate mightform an isolated defect, in which case this deformation is limited tothe region encompassing and surrounding a dust particle. Another exampleof an isolated defect in a laminate may be provided by a laminationinterface singularity (i.e., a singularity at an interface between thelaminated components) such as a scratch. Isolated defects are sometimesdefined by the rate of change in the local slope of a surface measuredwith a deflectometry-based technique developed by an automotiveconsortium and discussed by Fernholtz et al. atwww.speautomotive.com/SPEA_CD/SPEA2007/pdf/d/enabling_part1_paper4_fernholz_ford.pdf.

By way of distinction, however, the terms “extended defect” and“extended distortion” refer to a deformation of the surface of anoptical element, such that there exists no complete annulus, surroundingthe deformation, which annulus contains imperceptible excursion from themean figure of the surface. An extended defect in an optical element mayinclude such features as singular elongated scratches, creases and thelike as well as groups of similar defects. Extended distortion in areflecting surface may manifest itself by and be recognized through ameasured rate of change of curvature of the surface, or, equivalently, alocal change in optical power of the reflecting surface.

An optical element is said to be “substantially devoid of extendeddistortions” if the element, in its intended use, is substantially freeof extended distortions as visually perceived by an ordinary observer.For example, an image-preserving reflector including a laminate, whichhas extended distortions that reduce the quality of the image formed bythe reflector and that can be visually perceived by an ordinary viewer,is not “substantially devoid of extended distortion.” A stippled surfacereferred to as “orange-peel” provides an example of surface havingextended distortion. Visual requirements for automotive image-formingreflectors, including rearview mirror assemblies and those with back-updisplays, are based on the intended use where images of relativelydistant objects, viewed in reflection, are moving across the field ofview of the reflectors in a generally horizontal direction when thevehicles is in motion. Therefore, a reflector producing an acceptableimage for a closer and stationary object (such as a decorative roommirror, for example), may not yield an acceptable image for anautomotive application. Verification of whether variouslaminate-containing automotive image-forming reflector assemblies formimages that satisfy the visual requirements may be carried out withdifferent tests such as, for example, a test for visual distortionevaluation of a flat mirror as described in the DaimlerChryslerCorporation standard no. MS-3612 (referred to hereinafter as visualevaluation test). If, as required by this standard, an ordinary observerlocated at about 36 inches away from the reflector, does not seeblurring or fuzziness in the image of a 1 inch grid, consisting ofintersecting straight horizontal and vertical lines and placed at about15 ft in front of the planar reflector, such reflector will be perceivedas substantially devoid of extended distortions in its intended use.When performing a visual evaluation test, the observer will often movehis head relative to the mirror to assure that a slightly discernibledistortion of the image of the grid does not become objectionable forthe purposes of the mirror use. Such dynamic evaluation is not requiredby the MS-3612 standard. It is understood, however, that other standardsmay be applied in determining the fitness of the image-preservingautomotive reflector for its intended purpose.

A “first polarization” and a “second polarization opposite the firstpolarization” generally refer to two different polarizations. In aparticular case, the first and the second polarizations may beorthogonal polarizations (such as two linear polarizations representedby mutually perpendicular vectors, or left and right circular orelliptical polarizations).

A “light source” generally refers to a device serving as a source ofillumination inclusive of optical elements that may gate or shape theillumination. Thus, for example, an LCD or any other display illuminatedwith the light from a light emitter is included within the meaning of a“light source”. A light source may be used, e.g., for display ofinformation, video images, or for illumination of an object.

A “stand-alone” element of a mirror assembly is an element that, uponbeing fabricated, does not include any elements of the mirror assemblythat serve purposes other than the purpose of the stand-alone element.No component of a stand-alone laminate of the mirror assembly may be astructural element of any other subset of the mirror assembly. Astand-alone laminate, when fabricated, can be inserted into the mirrorassembly and removed from it without disturbing the performance of theremaining elements of the assembly. In comparison, a laminate mayintegrate another element of the mirror assembly: e.g., a substrate fora mirror component may be simultaneously utilized as a substrate for thelaminate, thus becoming one of the compound material components of thelaminate.

In reference to an optical component, being “opaque” implies havingtransmittance low enough to substantially conceal mirror assemblycomponents located behind the optical component. “Opacification”, inturn, refers to an act or process of rendering an optical componentsubstantially opaque.

A “depolarizer” is an optical structure that effectively changes a stateof polarization of polarized light transmitted or reflected by thedepolarizer into a different polarization state such that differencesbetween the fundamental polarization components of incident polarizedlight are reduced after passing through or reflecting from saidpolarizer. One example of a depolarizer for present purposes would be anideal depolarizer that scrambles the polarization of light and outputsrandomly polarized light whatever the input. A practical depolarizer ofthis type typically produces pseudo-random output polarization. Forexample, an element that randomizes the phase difference between the sand p components of incident linearly polarized light passing throughsuch element provides one example of a depolarizer. Another example of adepolarizer for present purposes would be a phase retarder convertinglinearly polarized light into elliptically polarized light such as,e.g., light polarized circularly, or into randomly polarized light. Theaddition of a depolarizer to the mirror assembly may result in a moreuniform distribution of intensity with a tilt angle in both reflectanceand transmittance when a viewer wears polarizing sunglasses. Inaddition, the presence of such depolarizer minimizes certain artifactsthat appear in reflected and transmitted images.

Types of rearview mirror assemblies that contain a display and to whichembodiments of the present invention may advantageously be appliedinclude, without limitation, mirrors comprising transflective elements(i.e. elements that are partially transmissive and partiallyreflective), reflective elements including prismatic reflectiveelements, and electrochromic mirrors. Transflective optics may be,without limitation, partially transmissive, multichroic,polarization-sensitive, or directionally transmissive. Various rearviewmirror structures and related methods of fabrication have beenaddressed, for example, in U.S. Pat. Nos. 5,818,625, 6,166,848,6,356,376, 6,700,692, 7,009,751, 7,042,616, 7,221,363, 7,502,156 andU.S. Patent Publication No. 2008/0068520, each of which is incorporatedherein in its entirety by reference. Displays and transflective opticsmay be incorporated in various vehicle locations, not only in rearviewmirrors (interior or exterior to the vehicle) and sideview mirrors, suchas sun visors, instrument panels, dashboards, overhead consoles and thelike. The rearview mirror assemblies may comprise surfaces of variousgeometries such as, by way of non-limiting example, planar, cylindrical,convex, aspheric, prismatic, other complex surfaces, or combinationsthereof. As schematically illustrated in FIG. 18 in side view, anembodiment 1800 of a typical automotive rearview mirror assemblycomprises a housing 1810 with a mirror system or assembly 1815 thatincludes a mirror element or subassembly 1820 and optional auxiliaryoptics 1830 such as, e.g., various filters affecting optical parametersof light. The mirror element 1820 may include an electrochromic elementor, e.g., a prismatic element. The mirror system 1815 is often used inconjunction with an electronic device 1840, e.g., a light source thatmay include a display 1850 such as an LCD, the light L from which may bedelivered through the mirror system 1815 towards a viewer 115 to producea displayed image visible to the viewer. Generally, the light source1840 may be disposed within the housing 1810 as a stand-alone componentbehind the mirror system 1815 as viewed by the viewer 115.Alternatively, the light source may be in physical contact (not shown)with the mirror system. Quite often contrast of a displayed image,perceived by the driver 115 through the mirror system 1815 against abackground of ambient light I reflected by the mirror system, may remainquite low, particularly when the ambient light I is plentiful. In someembodiments, the electronic device 1840 may be a light-detecting opticalcomponent for receiving light through the mirror system 1815.

A reflective polarizer (RP) may provide one class of possible solutionsto the recognized problem of transmitting a sufficient and optimizedamount of light from a display through the mirror system to the driver.A reflective polarizer substantially transmits light having one type ofpolarization while substantially reflecting light of the oppositepolarization. This may produce an effect of making the mirror systemessentially transparent to the polarized light L, generated by lightsource 1840, while maintaining a useful level of overall reflectance inunpolarized ambient light I incident upon the mirror system 1815. An RPmight be a linear polarizer, an elliptical polarizer or a circularpolarizer and might include an optical retarder such as a quarter-waveplate or a half-wave plate. A wire-grid polarizer provides one exampleof an RP. Alternatively, a reflective polarizer may include apolymer-based film structure comprising at least one opticallyanisotropic layer. Such polymer-based film structure is generallyreferred to herein as an anisotropic polymer-based film (APBF). Inreference to FIG. 22, an APBF may be incorporated within the mirrorsystem 1815 by laminating the APBF to one of the components of themirror system such as a glass substrate, for example. Alternatively, theRP may be used as an addition to the front polarizer component of an LCD1850 positioned behind the mirror system 1815. The RP may also be usedas a replacement for the front polarizer of the LCD. When the viewer 115wears polarizing glasses, it may be desirable to orient variouspolarizers within the embodiment 1800 of an automotive rearview mirrorassembly so as to optimize the relative intensities of the displayed andreflected images visible to the viewer.

For example, some automotive industry standards require only about 40percent reflectance for inside rearview mirror assemblies and about 35percent reflectance for outside rearview mirror assemblies. With the useof such mirror assemblies, the contrast of the illumination from adisplay, as perceived by the driver through a mirror system against abackground of ambient light reflected by the mirror system, remainsquite low, particularly when the ambient light is plentiful such as on abright sunny day. A commonly-assigned U.S. patent application Ser. No.12/370,909 filed Feb. 13, 2009, the entire disclosure of which isincorporated herein by reference, provides a discussion of the displaycontrast in a multi-zone mirror system having both opaque andtransflective areas. The contrast is defined as the ratio of theintensity of display-generated light reaching the viewer and theintensity of ambient light reflected by the mirror system. As shown inTable 1 for a mirror system having a transflective area with absorbanceof about 10% and an assumed 4,000 cd/m² raw display signal luminance and1,000 cd/m² ambient light luminance, the contrast of the displayincreases rapidly as the reflectance of the transflective area of themirror system decreases. Embodiments of the present invention, used inrearview mirror assemblies including a display device, may provide forthe display contrast that is greater than 1, preferably greater than 2,more preferably greater than 3, and most preferably greater than 4. Theuse of laminates comprising polymer-based films (such as an APBF) orother reflective polarizers in automotive rearview mirror assemblies mayfacilitate transmitting an optimized amount of light from the lightsource through the mirror assembly to the driver. For example, byaligning the polarization axis of the APBF with the polarization vectorof generally linearly polarized light delivered from a typical LCDlocated behind the mirror system, the losses of light from the displayupon passing through the APBF may be minimized. Consequently, theoverall amount of light transmitted from the display through the mirrortowards the driver tends to be increased. Teachings of such a conceptemploying an optically anisotropic polarizer (whether a conventionalwire-grid or a laminated foil made of multiple layers of plastic film atleast one of which is optically anisotropic, e.g. wherein some or all ofthe film layers have internal molecular orientation that induces adirectional difference in refractive index) are presented in U.S. Pat.No. 7,502,156. For example, a wire-grid polarizer, oriented within themirror assembly so as to transmit a substantial majority of the linearlypolarized light generated by a TFT LCD display located behind the mirrorassembly, would reflect up to about a half of unpolarized ambient lightincident upon the front of the mirror assembly and, therefore, providefor high visual contrast of the display on the ambient background.Examples of use of reflective polarizers in mirror/display devices arediscussed in WO 2005/050267, WO 2005/024500, and WO 2003/079318, each ofwhich is incorporated herein by reference in its entirety.

TABLE 1 Luminance of signal Luminance of reflected Contrast % T % R fromdisplay, cd/m² ambient light, cd/m² Ratio 10 80 400 800 0.5 20 70 800700 1.1 30 60 1200 600 2.0 40 50 1600 500 3.2 50 40 2000 400 5.0 60 302400 300 8.0 70 20 2800 200 14.0 95 50 3800 500 7.6

Various APBFs so far have been employed in energy efficient displayssuch as computer displays. Non-limiting examples of APBFs are providedby a multilayered polymer film comprising a body of alternating layersof a crystalline-based polymer and another selected polymer, or bymicro-structured film-based polarizers such as brightness enhancementfilms, or by dual brightness enhancement films (DBEF-E, and DBEF-Q, APF25, APF 35, APF 50, for example), all by 3M, Inc. (see, e.g., WO95/17303, U.S. Pat. No. 5,422,756), or by multilayered films containingalternating polymeric layers stretched in chosen directions. See SteveJurichich, Summary of The TFT LCD Material Report(www.displaysearch.com/products/samples/execsummary-materials.pdf); seealso 3M product description athttp://solutions9.3m.com/wps/portal/3M/en_US/Vikuiti1/BrandProducts/main/energyefficiency.

Fabrication of laminates comprising glass and polymer films has beenpreviously directed to safety glazing (see, e.g., U.S. Pat. Nos.3,471,356 and 4,277,299) and to windows that reject a portion of solarlight (so-called heat mirrors, see, e.g., U.S. Pat. Nos. 6,797,396 and7,215,473). The use of polarizing films for enhancement of reflectivityin a conventional viewing mirror was discussed, e.g., in U.S. PatentApplication No. 2007/0041096 and U.S. Pat. No. 7,551,354. However,fabrication of laminates containing plastic films for employment inrearview automotive mirror assemblies has not been addressed andpresents problems that significantly differ from those faced in thefabrication of the abovementioned conventional products. The differencesstem from the performance requirements imposed upon image-formingproperties of rearview automotive mirror assemblies by commonly acceptedindustry standards.

For example, a polymer film laminated between a glass substrate and aglass superstrate for use in safety glazing is generally not required topossess any special optical or mechanical properties other than meetingtransmission standards in visible light (i.e., at wavelengths betweenapproximately 380 nm and 750 nm). A typical safety-glazing laminate isused in transmission, and the index matching provided by such polymerfilm for the glass substrate and superstrate is known to facilitatevisual concealment of imperfections present at glass surfaces. Incontradistinction, in a case of a plastic-film-based laminate withintended use in a rearview mirror assembly, where the laminate includesglass lites and a functional anisotropic polymer-based film and operatesboth in transmission and reflection, the use of an additionalindex-matching layer may not necessarily conceal imperfections. On onehand, such index-matching layer added to the polymer film will affectoptical properties of the overall mirror system (e.g., reflectance,transmittance, and image-preserving properties such as ability to formundistorted images satisfying stringent standards of automotiveindustry). On the other hand, while possibly concealing the structuraldefects of glass surfaces, the index-matching layer may not necessarilyconceal the structural defects of the polymer film itself or defects ofthe lamination. Moreover, plastic film-based laminates used in safetyglazing do not utilize structurally anisotropic and often multilayeredfilms such as those employed in embodiments of the present inventionbut, instead, conventionally utilizes homogeneous films the materialproperties of which are uniform. Therefore, technical approachessuitable to safety glass manufacture are not applicable to solve theproblems of automotive mirror design.

Methods of conventional lamination of glasses and polymer films and theresulting laminates used in conventional applications mentioned aboveare well known. For example, typical flaws of a safety-glazing laminatemay involve occasional inclusions of contaminating material such asparticulates with dimensions on the order of a few microns that aresporadically scattered across, and embedded in, the safety-glazinglaminate and may be perceived by a naked eye as annoying visual defectsof the laminate. See U.S. Pat. No. 5,631,089. These flaws are examplesof isolated defects characterized by high spatial frequency that do notreduce the integrity and quality of the laminate for its intended use insafety glazing. As far as safety glazing applications are concerned,prior art does not consider low-spatial-frequency optical distortions,resulting from the lamination process, to be defects of the laminates.See, e.g., Laminated Glass Product Standards, atwww.viracon.com/laminatedStandards.html. Similarly, plastic filmscontained within heat-mirror laminates may not perfectly conform to thecurvatures of the underlying window glass and may form wrinkles, pleatsand even cracks in the functional layer. Although structural defects oflaminates used in heat-mirrors often lead to optical defects asdiscussed, e.g., in U.S. Pat. Nos. 7,215,473 and 6,797,396, each ofwhich is incorporated herein in its entirety by reference or atwww.cardinalcorp.com/data/tsb/1 g/LG02_(—)05-08.pdf, these laminatedefects are also known to not reduce the quality of the heat-mirrorlaminates for their intended use.

In contradistinction, structural defects in laminates used in anautomotive rearview mirror may significantly reduce the quality of suchmirror for its intended use. In fact, reflective polarizers such asAPBFs, used either as stand-alone components or in laminatedcombinations, have not been commercialized to-date in image-formingautomotive reflectors such as rearview mirrors, where the applicationrequires image-forming quality satisfying automotive standards.Moreover, prior art specifically acknowledges the drawbacks ofAPBF-containing conventional mirrors known to-date by teaching that suchreflectors produce inhomogeneities of reflection (both in color anddirection) that result in disturbed reflected images prohibiting the useof APBFs and APBF-containing combinations of elements (such as, e.g.,laminates) in automotive applications. See, e.g., U.S. Pat. No.7,551,354. The present application addresses these well-recognizedproblems and offers embodiments of APBF-based laminates and automotiverearview mirrors containing such laminates that satisfy existingautomotive standards.

In various applications, a primary purpose of a mirror is to form aclear and undistorted image. When a mirror assembly of interest is usedas a rearview automotive mirror, and the image of the environmentsurrounding the driver is distorted, the unwanted image aberrations maydistract the driver from correctly evaluating the traffic situation. Wehave empirically found that (in contrast to known applications such assafety glazing applications, or heat mirrors, for example), aconventionally performed lamination, with or without a cover plate, ofan APBF to a substrate in a rearview mirror assembly compromises thequality of the resulting mirror for its intended use. Such reduction inimage quality arises from lamination defects that are characterized bylow spatial frequency in a Fourier domain. These defects may bedescribed, in some embodiments, as detachments of the APBF from thesubstrate, rather considerable in size (generally on the order or amillimeter or more in at least one dimension) and substantiallydistributed across the resulting laminate's field of view (FOV). Oftenthese defects visually present themselves to an ordinary viewer as“stretch marks” in the laminated film. As a result of such sizeable, lowspatial frequency blemishes within a rearview mirror, an image of thesurrounding seen by the driver is at least distorted and may besignificantly aberrated in the portions of the rearview mirror affectedby the described shortcomings in the APBF lamination.

FIG. 1 schematically illustrates an example of extended distortions inthe context of a laminate 100 fabricated using conventional methods oflamination. The laminate 100 includes a substrate 102, a plastic filmsuch as an APBF 104, and a cover plate 106 and might be intended toserve to optimize the transmission of light 108 generated by an optionaldisplay 110 through a mirror structure 112 towards the user 115. Anymirror structure 112 that incorporates a conventionally-fabricatedAPBF-laminate 100 generally has a reduced optical quality, regardless ofwhether the assembly includes the display 110 or not. Lamination defects116 adversely affect the uniformity of reflectance across the FOV of themirror structure 112.

Arrows 118 and 120 indicate light incident on a proximal, as observed bythe viewer 115, side 124 of the mirror structure 112 and that reflectedfrom the mirror structure, respectively. The mirror structure 112 (or,similarly, any other optical quality image-forming reflector) thatincludes an APBF-laminate 100, appears to have an uneven surfacecharacterized by non-uniform and irregular low-spatial frequencywaviness and extended distortions 116. An image formed in reflectionfrom such a mirror appears, in turn, to be optically distorted, and, inthe automotive context, the mirror structure 112 would be deficient inproviding the driver 115 with an image of the scene behind the vehicle.An example of a reflector creating optical distortions that areprohibitive for automotive purposes is shown in FIG. 2. As shown, gridimage 200 is observed in reflection, according to a specified visualevaluation test, by the front of a Nokia N76 phone display that containsa polymer-film based laminate. FIG. 2 demonstrates distinctive bendingof lines and image warping perceivable by an ordinary observer. Thereflector of such quality would not be acceptable for the intended useof an automotive rearview mirror, for example.

FIGS. 3 and 7 schematically illustrate embodiments of a laminationprocess of the invention. In accordance with one embodiment of thepresent invention, processing steps are provided for the manufacture ofan image-preserving embodiment of this invention is now described withreference to FIGS. 3(A-G).

It was discovered that the ambient humidity at which the APBF is storedprior to the fabrication process and the humidity level maintainedduring the fabrication process may affect optical properties, structuralstability, and durability of the embodiments of the resulting laminates.In particular, the elevated levels of humidity during the pre-processingstorage generally led to increased haziness (and, therefore, to reducedtransmittance and increased scatter of light) in the fabricatedlaminates after the durability testing. Therefore, optionally, anembodiment of the fabrication process of the invention includes a stepof pre-lamination processing of the APBF (shown in a dashed line as step(A) in FIG. 3), during which the water content of the film is assurednot to exceed a chosen level. Characterization of haze levels wasconducted according to standards of the ASTM (American Society forTesting and Materials) and is discussed in more detail below. For aresulting laminate-containing embodiment of the invention to exhibittransmitted haze levels that are less than about 5% after thepost-fabrication testing (such as testing at 96 hours at 105° C.), theemployed APBF should preferably be stored, prior to the laminationprocess, at a temperature not exceeding about 40° C. and the relativehumidity (RH) less than 95% for less than 8 hours, or conditions thatlead to an equivalent water content change in the polymeric material.Similarly, in order to maintain haze levels below about 3% after thepost-fabrication testing, the film should preferably be stored at lessthan 40° C. and less than 95% RH for periods less than 4 hours.Similarly, to reduce transmitted haze to below about 1% after thepost-fabrication testing, the pre-processing storage temperature shouldpreferably be lower than 25° C. and at RH should be lower levels of lessthan about 30%.

Alternatively or in addition, to keep a pre-lamination moisture contentof the film within the preferred limits resulting in reduced haze of thefinal laminate, the APBF may be appropriately treated prior to thelamination process. Such treatment may include drying the APBF filmunder vacuum and elevated temperatures (approximately between 25° C. and40° C.) for at least 4 hours. It shall be appreciated that measurementsof moisture content in a given APBF can be carried out using differenttechniques. For example, a sample of DBEF-Q of a known area (e.g.,dimensioned to match the full size of the rearview mirror substrate) maybe precisely weighed and then subjected to particular storing conditionssuch as 40° C. at 95% RH, 40° C. in vacuum, or control ambientconditions (room temperature, open lab bench). The sample then may beprecisely weighed at known time intervals (e.g., 2, 4, 8 hours) todetermine the extent of weight gain or loss. The change in weight-% ofmoisture in the film is then determined from two weight measurements.The lamination processing and post-processing testing that follows allowfor correlating various optical properties, including transmitted hazelevels, of the laminate-containing embodiment of the invention with thedetermined initial levels of moisture content of the APBF. According toone embodiment of the invention it is preferred that the water contentof the APBF prior to lamination be less than about 0.6 weight-%, morepreferably less than about 0.4 weight-%, even more preferably less than0.2 weight-%, and most preferably less than about 0.1 weight-%.

During the fabrication process, an optionally pre-treated at step (A)APBF 302, which may be about 100 μm thick, is disposed, at step (B)(“Assemble a Composite”) of FIG. 3, on a surface of a substrate 304 asshown by an arrow 306. A superstrate 308 (also alternatively referred toherein as a cover plate) is then disposed over the APBF, which isindicated with an arrow 310, to form a composite 312. Although exemplaryembodiments of FIG. 3 are discussed with reference to an APBF, it shallbe understood that generally any other film may used for application tothe substrate 304 with a purpose of fabricating a laminate thatsatisfies automotive image-forming requirements, as described below.

In a specific embodiment, the substrate may be made of optical qualityglass or other materials suitable for use in an image-preservingreflector assembly and may be flat or have a selected curved shape. Theconfiguration of the superstrate 308 may be substantially the same asthat of the substrate 304, and surfaces of the substrate and superstratemay be conforming to each other. It should be realized, however, thatoverall dimensions of the substrate and superstrate are generally notrequired to be the same. In the context of rearview mirror assemblies, acomponent of the mirror system may perform as a substrate or asuperstrate for a laminate. For example, the mirror element 2220 of FIG.22 may be used as a substrate, and an additional lite of glass orappropriately chosen plastic (with optionally deposited opticalcoatings) may serve as a superstrate.

The polymer-based film 302 may be extruded or molded, or fabricatedusing other known methods, it may comprise a single layer (such as alayer of a low-density polyethylene, see, e.g., U.S. Pat. No. 5,631,089)or be a multi-layer film stack (such as a stack of alternating layershaving high- and low refractive indices) some of the layers of which maybe optically anisotropic (e.g., birefringent). For example, the film 302may contain commercially available plastics such as acrylics,polycarbonates, silicone, polyester, polysulfone, polycyclic olefin,PVC, or the like having nominal indices of refraction from about 1.3 toabout 1.8. The stack of layers with alternating refractive indices maybe used to enhance the reflectance of light having a given polarizationwhile simultaneously optimizing the transmittance of light havinganother polarization state. Such anisotropic layers may include, in oneembodiment, a prismatically microstructured surface similar to thatdisclosed in U.S. Pat. No. 5,422,756 that facilitates the separation ofthe incident light into two components having orthogonal polarizations.In addition or alternatively, the film 302 may comprise a plurality ofalternating polymeric layers of at least two types having, respectively,high and low refractive indices at one polarization and different highand low refractive indices at an orthogonal polarization. One example ofsuch film, comprising alternating layers of crystalline naphthalenedicarboxylic acid polyester, was described in WO 95/17303. In yetanother alternative embodiment, the multilayer polymer film 302 maycomprise a layer that has a spatially oriented structure realized, forexample, by stretching an otherwise isotropic polymer film in a chosendirection.

It should be noted that, to assure adequate flattening of the film 302between the plates 304 and 308 at the step (B) of FIG. 3, the film maybe optionally put under tension. For example, the film 302 may beuniformly stretched in radial directions at about 0.1 oz. to about 60lbs per linear inch. In some embodiments, the preferred tension may bebetween about 1 and about 10 lbs per linear inch. In one embodiment, theinitial application of the optionally stretched polymer-based film 302onto the substrate can be complimented with using a soft press roll at anip pressure of about 5 to 500 psi to assure that the film 302 conformsto the surface of the substrate 304.

During the “Laminate/Bond” step (C) of FIG. 3, heat, pressure, andoptionally vacuum are applied to the composite 312. In general, thecomposite may be vacuum-bagged, evacuated, and autoclaved under pressurefor time sufficient to bond the film 302 to at least the substrate 304without forming spatially extended lamination defects described aboveand to form a substantially image-preserving laminated opticalcomponent. It was unexpectedly discovered that application of pressureto the surface of the composite at elevated temperatures, as discussedin the literature, may not be adequate for ironing out the imperfectionsand wrinkles from the film 302 for the purpose of producing a laminatepossessing optical qualities that satisfy automotive industry standards.One possible solution to this problem is to apply substantiallyomnidirectional pressure (such as that attained in a pressure autoclave)to the laminate composite. Processing parameters and the resultinglaminates are further discussed below. Following the application of heatand substantially omnidirectional pressure, the laminate is formed. Inthe embodiment 314 of the laminate of FIG. 3(D), for example, thepolymer film 302 is shown to have adhered to both the substrate 304 andthe superstrate 308. In a specific embodiment, no adhesive is usedbetween the layers 302, 304, and 308 of the composite 312 during thelamination procedure. Although the presence of adhesive along a surfacewithin the laminate structure does not change the principle of themethod of the invention or the resultant construct/assembly, it wasunexpectedly found that laminates formed with substantially no adhesivealong at least one lamination interface between the plastic film and thecover plates tend to have higher probability of producingimage-preserving rearview mirror assemblies of optical quality definedby automotive standards.

In a related embodiment, a superstrate portion 308 of the laminate maybe removed, as shown at an optional step (E), “Release Superstrate”, forexample after the lamination has been complete but prior to the qualityinspection step of the process of the invention. As shown in FIG. 3(F),the polymer-based portion 302 of the laminate 316, which resulted aftera superstrate release, has an exposed surface 317. To facilitate arelease of the superstrate 308 at the “Release Superstrate” step (E) ofFIG. 3, the superstrate may be appropriately treated, prior to the“Assemble Composite” step (B) of FIG. 3, according to any method knownin the art to prevent it from being permanently adhered with the filmstructure 302. For example, in reference to FIG. 3(A), a suitable filmor coating (also referred to as a release layer) may be applied to theinner surface 318 of the superstrate 308 facilitating the removal of thesuperstrate and allowing for the APBF 302 to remain attached to thesubstrate 304. Alternatively, the inner surface 318 may be treated witha release-facilitating chemical agent such as, e.g., an alkylsilane, orany of the commercially available silicone or wax-based release agents.It has been discovered that these various release agents do notfacilitate formation of visibly perceivable defects in the laminate anddo not appreciably impede transmission of light through the laminate. Inaddition or alternatively, the surface 317 of the polymer-based film 302may be similarly treated prior to the assembly of the composite. As aresult, the superstrate 308 is releasably adhered to the film 302 andcan be easily removed either manually or automatically.

To enhance adhesion of the DBEF or other APBF to a desired substrate orsuperstrate and to improve durability of the resulting laminate, thesubstrate and/or the superstrate is preferably cleaned (not shown)before the lamination process to remove contaminants which couldinterfere with adhesion and induce optical defects. Cleaning can beaccomplished chemically using detergents, solvents, or etchants toremove gross contamination. In addition or alternatively, mechanicalcleaning of a substrate may be employed using polishing compounds suchas aluminum oxide or cerium oxide can be used to further prepare thesubstrate surface. In addition, at least one of the substrates and thepolarizing film can be optionally pretreated (not shown) to enhanceadhesion. Surface treatment such as with flame, ozone, corona plasma, oratmospheric plasma can be used to further clean and/or functionalize thesurfaces to be bonded. Adhesion promoters or coupling agents such asorganofunctional silanes, organotitanates, organozirconates,zircoaluminates, alkyl phosphates, metal organics or adhesion-promotingpolymers can be deposited in a thin-film form using a variety oftechniques. These promoters and coupling agents are used to bridge theinterface between the inorganic and organic substrates and improveoverall adhesion and resistance to humid environments. Examples ofsuitable adhesion promoters include Z-6011 silane (from Dow Corning) andSilquest A-1120 silane (from G.E. Silicones).

It shall be also understood that in an embodiment where the superstrateis removed (or released) and thus does not remain part of the laminate,the superstrate generally does not have to be made of a transparentmaterial. In such embodiment, various superstrate materials can besuitably used such as, e.g., ceramics, metals, carbide, boron-nitride,fluorocarbon, phenolic, acetal or nylon. Moreover, in such embodiment,at the initial steps of fabrication of a laminate, the use of asuperstrate 308 may not be required at all.

FIG. 7 illustrates some alternative embodiments pertaining tointermediate steps of fabrication of a laminate with and without asuperstrate. As shown in FIG. 7(A), for example, an arm 702 of apressing mechanism may be made of a material suitable for release fromthe polymer portion 302 of the laminate and is withdrawn after thebonding step of the process. Therefore, the arm 702 itself may performas a superstrate 308 releasable from the laminate 316 of FIG. 3(E)during the laminate fabrication cycle. In comparison, as shown in FIG.7(B), a superstrate 308 may be initially attached to the arm 702 andremain a bonded part of laminate 314, prior to being released. FIG. 7(C)illustrates fabrication of the embodiment of the laminate using apress-roll 704. As was mentioned above, in some embodiments, to assurethat the quality of the laminate satisfies the imposed image-preservingrequirements, applying omnidirectional pressure may be preferred toapplying pressure otherwise. The lamination of the DBEF in an autoclavehas been shown to assure processing conditions adequate to modify theoptical quality of the DBEF for use as a high quality specularimage-preserving reflector. The DBEF or other APBF itself can beoptionally pre-processed prior to attachment to the mirror element. Aweb method for pre-processing the APBF for higher optical quality is topass the APBF compressed between one or more pairs of rollers that maybe optionally heated. This optional treatment facilitates flattening ofthe film and may be used in addition or as an alternative to stretchingthe film, as discussed above. The flattened APBF can then be laminated.

(1) Heat-Press Operation: An APBF-including composite (such as, e.g.,the composite 312 of FIG. 3(B)) may be initially placed cold in a pressand then heated under substantially omnidirectional pressure to a finalprocessing temperature, in accordance with step (C) of FIG. 3.Generally, the applied pressure may be varied based on the processingtemperature. By way of example, one embodiment may include a two-stepprocessing, when a composite that is kept at some predetermined initialpressure may be heated to a preferred processing temperature at thefirst step. At the second step, once the preferred processingtemperature has been reached and maintained, the pressure is ramped upas a chosen function of time. Alternatively, at the first step, thepressure applied to the composite may be ramped up as a chose functionof time at a constant level of temperature, and then, at the secondstep, the temperature may be ramped up to a preferred operational levelwhile the level of pressure is maintained. Alternatively, the compositemay be first preheated to a fraction of the final processingtemperature, then appropriately pressed and heated further to the finaltemperature. Various other options of changing temperature and/orpressure with time, simultaneously or separately, are contemplated asembodiments of the present invention. Optionally, the cover plates 304and 308 and the APBF 302 may be first each preheated to some fraction ofthe final processing temperature, then assembled with an APBF into thecomposite 312, which is further exposed to pressure and heated to thefinal processing temperature. Optionally, the cover plates 304 and 308and the APBF 302 may be heated to final processing temperature, thenassembled into the composite and further exposed to the requiredpressure. If a press is used, the press anvil(s) may be flat or profiledand made of a compliant material and designed to apply force asrequired.

(2) Oven/Roller System: The composite such as composite 312 of FIG. 3(B)may be placed in a cold oven, heated to the final processingtemperature, and pressed in at least one roller press. Alternatively, atleast one of the cover plates 304 and 308 may be preheated to a fractionof the final temperature, following which the composite with the APBF isassembled, then pressed in at least one roller press and heated to thefinal processing temperature. Optionally, the components of thecomposite may be heated to the final processing temperature, assembledinto the composite, and the roll-pressed. Press rollers used may be flator profiled to apply force as required.

(3) Sonic Heat Press and Inductive Heat Press provide alternativefabrication approaches. For example, heating at least one of the coverplates 304 and 308 and the film 302 during the lamination process may beaccomplished ultrasonically. A sacrificial film (e.g., a film disposedbetween the APBF and an anvil in the embodiment of FIG. 7(B)) may beused to preserve the cosmetics or functionality of the APBF. Heating mayalso be accomplished inductively using the transparent conductive oxide(TCO) or metal films that are adjacent to the APBF and operate as theheating element to attain at least a fraction of the final processingtemperature. For example, the components to be laminated may beconventionally preheated to some portion of the final temperature, thenpressed and inductively heated. The inductive heating and pressing maybe advantageous in allowing for selective sealing of the APBF tosubstrates that have conductive properties. The press anvil(s) used maybe flat or profiled to apply force as required.

At a post-lamination processing step (G), shown in FIG. 3, the qualityof embodiments of a fabricated laminate (such as the laminate 314 havingan APBF sandwiched between two cladding elements or the laminate 316having the film bonded to only one cladding element) may be verifiedvisually or by using an appropriate measurement technique. For example,a wave-scan device from BYK-Gardner (see www.byk.com), such as the“wave-scan dual” may be readily adopted for measuring through thesubstrate or superstrate, the quality of the lamination interfaces.Defects in an interface formed by laminated or bonded surfaces may becharacterized based on sizes of the lamination defects, with respect toif and how these defects affect the clarity of the image obtained inreflection from such interface. In particular, the BYK-Gardnermeasurement system uses a “short wave”, or SW, designation for detecteddefect features having dimensions from about 0.1 mm to approximately 1.2mm and a “long wave”, or LW, designation for detected distortionfeatures of 1.2 mm to approximately 12 mm in size. (Characterization insmaller dimension ranges is also possible). The values SW and LW areprovided on a normalized scale from 0 to 100, where lower valuescorrespond to smaller structural distortions and waviness of thelaminated interface than higher values. Using this measurementtechnique, it has been empirically found that a reflector suitable formost non-automotive applications should be characterized by SW and LWvalues less than about 10, preferably less than about 7, more preferablyless and 5, and most preferably less than 3. In contradistinction,image-preserving reflectors with intended use in rearview automotivemirror assemblies (including those containing laminated interfaces)should preferably be characterized by SW and LW values that are lessthan 3, more preferably less than 2, and most preferably less than 1. Itis understood, however, that various other optical techniques such asinterferometric profilometry, or measuring of light scattering, or anyother known in the art approach suitable for surface characterizationmay be alternatively used to describe the quality of the laminatefabricated according to an embodiment of the method of the invention.

For example, quality of the APBF-based laminates and mirror structurescontaining such laminates can be characterized with the use of ONDULOtechnology developed by Visiol Technologies (France) based on theprinciple of phase shifting deflectometry and commonly used inautomotive industry for evaluation of visual defects occurring when twopanels are bonded together. The goal of this non-contacting technique isto quantify the structural defects in inspected reflecting interface(whether curved or flat) based on distortions of the reflection of afiducial object in that interface. Based on the evaluation of suchdistortions, the data are generated representing spatial derivatives ofthe slope of the surface of the reflector, and a conclusion of the typeand distribution of structural defects in that reflector is obtained.The metric used for evaluation of the optical distortions with thistechnology is defined as “Curvature Units” (CU). The advantage of usingthe deflectometry approach is its high spatial resolution, the abilityto recognize both isolated, point defects and extended defects, and agood correlation with visual tests. We have empirically found thatimage-preserving laminates with intended use in rearview automotivemirror assemblies should be characterized by CU values with moduli notexceeding approximately 0.04, preferably no exceeding 0.03, morepreferably not exceeding 0.02, and most preferably not exceeding 0.01.An alternative technique for quantifying medium and small scale defectsin an embodiment of a laminate of the invention may be based on a(local) measurement of a difference in optical powers of a flatreflecting surface and that of a flat reference surface, caused by thepresence of structural defects in the reflecting surface. See, e.g., adescription by ISRA Vision AG at www.isravision.com. In this technique,a set of fiducial lines is projected onto the tested reflecting surface,moved in front of the computerized line-scan detector that captures andanalyzes the reflected image in comparison with a reference image. Aconclusion about the surface defects is expressed in units ofmillidiopters of optical power of the surface under test. According tothe embodiments of the present invention, image-preserving laminateswith intended use in rearview automotive mirror assemblies and measuredusing ISRA approach are characterized by local optical power values ofless than 1,000 millidiopters, more preferably less than 750millidiopters, even more preferably less than 500 millidiopters, andmost preferably less than 250 millidiopters.

The following discussion provides some examples of lamination processesand the resulting laminate structures, obtained according to theembodiments of the invention for the intended use in automotive rearviewmirror assemblies. Generally, the temperature T selected to laminate aninitial composite is within a range from about 50° C. to about 160° C.,preferably between about 80° C. to about 150° C., and most preferablybetween about 90° C. to about 110° C. The levels of substantiallyomnidirectional pressure P chosen for lamination are between about 25psi to about 2,500 psi, preferably from about 50 psi to about 500 psi,and most preferably from about 100 psi to about 400 psi. The weightcontent of water in an APBF to be laminated is maintained as discussedabove. The lamination time can generally vary between about 1 and 600minutes, preferably between 5 and 180 minutes and most preferablybetween 15 and 60 minutes. However, different processing parameters maybe used, provided that the quality of the optically active,polarization-affecting layer of the APBF is not compromised. Optimaltime, temperature, humidity, and pressure generally depend on the choiceof materials used in fabricating the APBF and particular media used inan autoclave. In some embodiments, the use of liquid in an autoclaveimproves the uniformity of temperature across the composite and improvesheat transfer.

In one embodiment, for example, a glass-plastic composite of about 55 mmby 75 mm in size was formed by sandwiching an APBF reflective polarizingfilm (from Nitto Denko corporation), having a thickness of about 2 milsand a pressure-sensitive adhesive on one of its sides between a 1.6 mmthick substrate and a 1.1 mm thick superstrate, with the film's adhesiveside facing the superstrate. The laminating process included assemblinga composite at preferred levels of water content in the film and vacuumbagging the composite, followed by autoclaving at the temperature ofabout 90° C. and a gauge pressure of about 200 psi for 1 hour. Both thevisual image testing, as described above, and the wave-scan BYK-Gardnertesting confirmed that the quality of the laminate was satisfactory forits intended purpose in the automotive rearview mirror assembly. Inparticular, the wave-scan measurement of the laminated glass-polymerinterface through the substrate produced normalized averaged surfacefigures of about SW 0.4 and LW 0.8 for the first and the seconddimensional ranges of features measured by the BYK-Gardner device. Whenan APBF has a surfaces with different texture, it may be advantageous toform a laminate in such a fashion as to have this smoother side later onplaced towards the observer in the overall rearview mirror system.

In further reference to FIGS. 3(A-G), we have discovered that, in orderto facilitate a defect-free fabrication of a laminate containing thefilm 302 that is multi-layered, it may be preferred in some embodimentsto have the cladding or adjacent layers of the multilayer film 302comprise materials having different glass transition temperatures orother properties. In other words, prior to fabrication of anAPBF-containing laminate, a targeted engineering of an APBF componentmay be required to improve at least one of adhesion and opticalproperties to obtain a laminate that is substantially free of extendeddistortions and that meets the environmental requirements and therequirements on the quality of optical image. In one embodiment, theAPBF may include a three-layer or a multi-layer film structure with atleast one core optically anisotropic layer having high T_(g) (e.g.,T_(g,score)˜140° C.). that is sandwiched between two or more generallydissimilar cladding layers each of which has a corresponding different(e.g., lower, T_(g, clad)<T_(g, core)) glass transition temperature anddifferent material and mechanical properties such as hardness. Informing the laminate composite with such multi-layered APBF structure,where the cladding layers are placed in contact with components servingas a substrate and a superstrate of the composite, the laminationprocess may be advanced in several ways. First, an appropriate choice ofmaterials for cladding layers may assure that the core, anisotropiclayer of the APBF is sufficiently flat and would not be crumpled betweenthe glass plates during the lamination. In one embodiment of the presentinvention, the plastic-based cladding layers of the multi-layered APBFare chosen to possess a hardness value of at least Shore A 70, asmeasured with methods known in the prior art. In another embodiment, thehardness if at least Shore A 80 is preferred. Second, it was discoveredthat the lowest glass transition temperature (among the transitiontemperatures of the cladding layers) generally correlates with thepreferred lowest suitable lamination temperature. Therefore, in oneembodiment of the invention, during the lamination of a multi-layeredAPBF between a substrate and a superstrate such as those made of glass,the amount of heat applied to the composite of 312 of FIG. 3(B) could bedefined, for example, by a temperature exceeding the lower limit of theapplicable dynamic range of glass-transition temperatures. The optimaltemperature for laminating a composite containing a multilayered APBFwas found to be generally between a first temperature value (that isabout 10° C. below the onset of the lowest temperature within thedynamic range of glass transition temperatures) and a second temperaturevalue (that is about 10° C. higher than the highest temperature withinthe dynamic range). Multi-layered APBFs engineered for the purposes oflaminates with intended use in automotive rearview mirror assemblies maybe more complex. For example, a core, optically anisotropic layer of amultilayered APBF may itself include multiple isotropic and birefringentlayers. Optionally, one of the cladding layers of the multi-layered APBFfilm structure may be a depolarizing layer employed to depolarize aportion of the display-generated light and/or the light reflected by themirror assembly.

A major effect of adding a depolarizing component to a reflectivepolarizer in a conventional application is considered in a prior artbacklighting system, where a reflective polarizer was shown to enhancethe perceived brightness of the LCD. To achieve such enhancement, thereflective polarizing film was placed between a light emitter and an LCDin such a fashion as to align polarization of light transmitted from thelight emitter through the reflective polarizer with a direction requiredfor optimal operation of the LCD. It will be realized that the additionof a depolarizing component to such a system between the reflectivepolarizer and the LCD (i.e., on the other side of the RP as seen fromthe light emitter) reduces a degree of polarization otherwise resultingwhen only the reflective polarizing film is present. This situation isillustrated in FIG. 23. Indeed, in this case, polarization of lighttransmitted from the light emitter towards the LCD through a sequence ofthe reflective polarizer and depolarizer would be substantiallyrandomized, and the overall backlighting display system would to anextent operate as if the combination of the reflective polarizer anddepolarizer were not placed between the light emitter and the LCD atall. As shown, an RP 2310 is used to optimize transmission ofunpolarized light from a light emitter 2320 through an LCD 2340 in aconventional display application by re-circulating a portion of theemitted light between the RP 2310 and a reflector 2350, positioned onthe opposite sides of the light emitter 2320. in a fashion described inpriori art. Here, the addition of a depolarizing component 2360 negates,to some extent, the benefit provided by the RP. In contradistinctionwith conventional applications such as the backlighting application, theuse of a combination of the RP and depolarizer in one embodiment of theinvention provides certain advantages, as discussed below. Specifically,the resulting embodiment of a rearview mirror is not only characterizedby optimized transmittance of light from the light source through themirror system but it also performs in a fashion substantially unaffectedby angle effects otherwise typically noticed by an image observer (suchas a driver) wearing polarized glasses.

In a specific embodiment of the invention, at least one of the substrateand superstrate of the laminate may be made of plastic. The resultinglaminate may be used, e.g., as a stand-alone component within the mirrorsystem to provide an image-preserving rearview mirror satisfying theautomotive standards. In this embodiment, plastic materials may bechosen to have corresponding glass transition temperatures exceeding theoptimal temperature used in the lamination process. Examples of suchmaterials are polycyclic olefin, polycarbonate, acrylic, polyimide,polyether-sulfone or epoxy. It shall be understood, however, that anyother material suitable for use, in an image preserving reflector, as asubstrate or a superstrate for a polymer-based film laminate can beused. In an embodiment where a superstrate of the laminate is notreleased, a component of the mirror system performing the role of thesuperstrate and positioned between the display and the reflectivepolarizer should preferably be formatted to not substantially depolarizelight.

Once the lamination interface has been formed, it may be optionallyprotected (not shown in FIG. 3) from oxygen, water, or othercontaminants by having the edge of the laminate sealed. If necessary,the film may be cut slightly smaller than the substrate and superstratethus providing a notch therebetween for the sealing material to reside.Sealing may be accomplished with a variety of crosslinked materials suchas moisture cured materials, thermoset or UV cured materials, preferablywith materials having low curing temperatures. Silicones, epoxies,acrylates, urethanes, polysulfides provide but a few examples of suchmaterials. Additionally, thermoplastic materials such as warm or hotmelt polyamides, polyurethanes, polyolefins, butyl rubber,polyisobutylene and the like may be used for the purpose of sealing thelaminate. Examples of suitable sealing materials include LP651/655 (fromDELO, Germany) and the Eccoseal series of sealants (from Emerson &Cuming).

Embodiments of laminar structures provided by the process of theinvention (e.g., the embodiments 314 and 316 of FIGS. 3(D) and 3(F),respectively) are useful in image-preserving and image-forming reflectorassemblies such as rearview automotive mirrors, which form imagessubstantially free of extended distortions because of the quality of theemployed laminar structures. For example, as shown in an embodiment 400of an electrochromic dimmable mirror assembly of FIG. 4(A), the APBF 302is laminated to the embodiment 402 of an electrochromic element(discussed with reference to FIG. 7 of the commonly-assigned U.S. Pat.No. 7,009,751, the disclosure of which is incorporated herein in itsentirety) between the rear surface 114 b of the rear element 114 of theEC-element and the light source 170, which may be a backup display. Inan alternative embodiment, however, a laminate of the invention can beadvantageously used with other types of reflecting structures. As shownin FIG. 4(B), e.g., the laminate 314 of FIG. 3(D) may be employed as astand-alone component within a non-dimming tilt prism-mirror structure404 (including a tilt prism element 408), behind which there may beoptionally positioned an information display (not shown). Alternatively,a tilt prism element assembly 410 may incorporate an RP (APBF) element302 that is laminated to one of the components of the tilt mirroritself, as shown in FIG. 4(C). As shown in an embodiment 420 FIG. 4(D),a liquid crystal cell or device 422 capable of modulating light, such asa Twisted Nematic (TN) cell, a Super Twisted Nematic (STN) cell, a guesthost or phase change LC device incorporating a dichroic dye, aFerroelectric LC device, a Distortion of Aligned Phases (DAP) LC deviceor other LC-cells known in the LC art can be placed in front of the RP(APBF) element 302 to modulate the ambient light 118 incident upon theproximal side 124 of and reflected by the mirror system 420 and/or lighttransmitted through the system 420 from a light source disposed behindthe distal, with respect to the observer, side 424 of the system 420. Itwill be appreciated that, although the embodiments of FIGS. 4(B) through4(D) are shown as employing a prismatic mirror element, similarembodiments may employ dimming mirror structures such as thosecontaining electrochromic elements. In a specific embodiment,schematically shown in FIG. 4(E), the RP 302 may be laminated directlyto the LCD subassembly 1850 or some components of the LCD subassemblyand then to the mirror element 1820 (which may include a prismaticoptical element or an electrochromic element) so as to optimize thenumber of optical interfaces present and improve the overall reflectanceand transmittance properties of the rearview mirror system. In anotherembodiment it may be useful to include an additional layer of PSAcontaining a UV-blocking agent, or a UV-blocking polymer film in frontof an APBF, as seen by the observer. The addition of such UV attenuatingagents or blockers may prevent visual degradation of the APBF and/ordegradation of the integrity of the APBF-containing laminate. Inembodiments where the APBF is located behind the electro-optic cell suchas an EC-element or a cholesteric element, it is possible to dispose theUV-attenuating agents within the electro-optic cell. Cholesteric devicesand EC-elements including these agents are taught, respectively, in acommonly assigned U.S. Pat. No. 5,798,057 and in commonly assigned U.S.Pat. No. 5,336,448 and U.S. Pat. No. 6,614,578, each of which isincorporated herein in its entirety.

Reflecting structures and assemblies such as rearview mirrorsincorporating polymer-based films laminated according to the embodimentof the invention generally do not exhibit optical blemishes, are devoidof extended distortions, and do not produce image distortions thatdistract the viewer, as discussed above, thus preserving the quality ofoptical imaging within the requirements of automotive industrystandards. Although embodiments of the invention are discussed in thisapplication with respect to placing an APBF-containing laminate of theinvention in particular locations within a rearview mirror assembly, itwill be noted that, generally, positioning a laminate of the inventionin other suitable locations is also contemplated. In one embodiment ofthe rearview mirror, e.g., an additional APBF-containing laminate may bedisposed behind the display, as seen by the observer.

In a specific embodiment, an air gap or cavity can be formed betweensurfaces of the mirror system and later preferably sealed with aperimeter seal to avoid entrapment and/or condensation of vapors anddust. For example, a mirror assembly may include constructions such as[G/RP/air/G] or [G/RP/G/air/G/ITO/EC/ITO/G]. In these exemplaryconstructions, the components or media are listed starting with the onefarthest from the viewer, the “air” denotes a cavity or a gap that maybe defined by the perimeter seal and/or spacer disposed between theadjacent components separated from one another, “RP” refers to a layerof reflective polarizer such as APBF, for example, and “G” denotes alite of glass or other suitable substrate material. FIGS. 4(F) through4(H), schematically showing embodiments of a mirror assembly employing aprismatic mirror element, provide several non-limiting examples of suchconstruction sequences. FIG. 4(F) illustrates a prism-based embodimentthat relates to the embodiment of FIG. 4(C), but in which the prism 408is spatially separated from a laminate 316 containing the RP 302 and theglass substrate 304 by an air-filled cavity 435 formed with the use of aperimeter seal and/or spacer 438 placed between the prism 408 and the RP302. The corresponding construction sequence may be described as[G/RP/air/prism]. FIG. 4(G) provides an alternative embodiment includingthe air-gap 435, in which the laminate 314 is formed by sandwiching theRF 302 between two lites of glass 304,308, as previously discussed. Thecorresponding construction sequence may be described as[G/RP/G/air/prism]. Shaping the air cavity 440 as a wedge, as shown inFIG. 4(H), provides an additional benefit of constructing an embodiment442 of the mirror assembly with the use of only standard, off-the-shelfglass plates (304, 308, and 444). The sequence of components and mediacorresponding to the embodiment of FIG. 4(H) may be listed as[G/RP/G/prism-shaped air/G]. The wedge-shaped cavity 440 may be formed,for example, by disposing the laminate 314 and the plate 444 at anappropriate angle A and sealing the non-uniform peripheral gap along theedge of the plates 304 and 444 with a perimeter seal. It would beappreciated that any air-gap (including the wedge-shaped air-gap), onceformed, may be filled with a clear adhesive material (such as urethane,silicone, epoxy, acrylic, PVB or equivalent materials), liquid (such asmineral oil, glycol, glycerin, plasticizer, propylene carbonate or thelike), or gel, if desired. In constructing such prismatic mirrorstructures, supplemental transparent layer and opaquereflectance-enhancement layers can be applied to any substrate surfaceother than the surface closest to the viewer. Enhancement of reflectancecharacteristics of the embodiments of the invention is discussed below.The air cavity may be formed in other locations as desired, e.g.,between the flattened reflective polarizer and a substrate element. In arelated embodiment, the optically anisotropic film used in a laminatemay be cast, coated or fabricated directly onto the optically flatsubstrate or glass and may not require further processing to achieveoptical characteristics desired for use as a high quality mirror such asan automotive rear-view mirror. Any component used as a substrate or asuperstrate for the APBF must possess optical quality to pass alloptical requirements corresponding to the intended use of the finalproduct.

A simplified scheme, not to scale, of an embodiment 600 of the mirrorassembly is shown in FIG. 6 in a cross-sectional view. The APBF film602, which is a part of the laminate 606 shared with the EC-element 608,is a 5 mil thick DBEF-Q film manufactured by 3M Inc. A substrate 610 ofthe laminate 606 includes a 1.6 mm thick soda-lime glass plateperforming as a back plate for an approximately 137 μm thick chamber 614that contains EC-medium. A superstrate 620 of the laminate 606 includesa 1.6 mm soda-lime glass plate 620 that is overcoated, on the surface624 facing the APBF film 602, with a thin-film stack 630 including, inthe order of deposition, approximately 450 Å of titania, TiO₂, andapproximately 150 Å of indium tin oxide, ITO. The chamber 614 containingthe EC-medium is formed by the back glass plate 610 (having surfaces 632and 634) and a front glass plate 635 (having surfaces 636 and 637). Eachof the plates 610 and 635 is coated, on the respective surfaces 632 and637 facing the chamber 614, with a transparent conductive coating suchas ITO (the half-wave optical thickness of which may be chosen at aselected wavelength or as a mean value for a spectrum, for example).Some embodiments of the EC-chamber are discussed in a commonly assignedU.S. Pat. No. 6,166,848, which is incorporated herein by reference inits entirety. Another surface of the plate 610—surface 634—is coated, inthe area outside of the laminate assembly as viewed along the z-axis,with a thin-film stack 638 comprising chromium-ruthenium-chromiumlayers, as described in U.S. Pat. No. 7,379,225. The variousabovementioned thin-film layers can be fabricated by a variety ofdeposition techniques such as, for example, RF and DC sputtering, e-beamevaporation, chemical vapor deposition (CVD), electrodeposition, orother suitable deposition techniques. Embodiments of the invention arenot limited to using a given deposition method for these or other thinfilm coatings.

As discussed above, the display assembly 639 may be optionally disposedbehind the laminate 606 (i.e., adjacent to the surface 640 of the plate620). In such a case, the embodiment 600 may be viewed by the observer115 as exhibiting three distinct areas: the transflective, “display”region 642, through which light generated by the display assembly maypropagate through the laminate 606 and the EC-chamber towards theobserver, and the outer, reflective region(s) 644 adjacent to thetransflective region. As shown in FIG. 6, the APBF 602 covers only adisplay portion 642 of the mirror structure 600. In a relatedembodiment, the APBF 602 and/or the resulting laminate 606 may cover thefull FOV of the mirror assembly, i.e. both the display zone 642 and anopaque zone 644. In such an embodiment, all of the surface 634 of theplate 610 may be laminated over with the APBF. Table 2 lists therelative color and brightness characteristics, according to CIELAB, forthe display and opaque regions, 642 and 644, respectively, of thelaminate-containing reflector described in reference to FIGS. 5 and 6.Display (transflective) area of the mirror system: L*=76.7, a*=−2.7,b*=−1.8, Y (percent reflectance)=51%, Opaque (non-display) area of themirror system: L*=77.5, a*=−2.3, b*=1.1, Y=52.5%.

TABLE 1 (Adjacent) Display Area Opaque Area L* 76.7 77.5 a* −2.7 −2.3 b*−1.8 1.1 Y 51% 52.5%

From the position of the observer 115, the surfaces 636, 637, 632, 634,624, and 640 of the structural elements of the assembly such as glassplates are viewed as the first, the second, the third, the fourth, thefifth, and the sixth surfaces, respectively, and may be alternativelylabeled with roman numerals as I, II, III, IV, V, and VI, as shown inFIG. 6, to indicate their position with respect to the viewer. In thisembodiment, surface I corresponds to a front, or proximal, side of theEC-mirror element and surface IV corresponds to a rear, or distal, sideof the EC-mirror element, with respect to the observer. Generally, thechosen surface numbering applies to any embodiment of the presentinvention. Specifically, surfaces of the structural elements (such assubstrates) of an embodiment of the invention are numerically labeledstarting with a surface that is proximal to the observer.

The use of the APBF-containing laminate in conjunction with a lightsource in a rearview mirror assembly, for the purposes of increasing theeffective brightness of the light source on the background of theambient light, may be particularly advantageous when the employed lightsource generates polarized light that is preferentially transmitted bythe APBF. Light sources emitting either partially or completelypolarized light—such as displays equipped with an LED, or a laser diode,or an LCD—provide particularly suitable examples. When the displayassembly 639 comprises an LCD, the front polarizer of the LCD may bereplaced with the laminate of the invention. In an alternativeembodiment, a substrate of the LCD, through which light exits the LCD,may be used as a superstrate for a laminate of the invention. In thiscase, a reflective polarizer included within the laminate of theinvention may be used to transmit light having the first polarizationand generated by the display located behind the laminate, and to reflectlight having a second polarization that is orthogonal to the firstpolarization.

Referring again to FIG. 6, a series of laminates 606 were fabricatedusing an embodiment of the process of the invention that included atleast (i) vacuum bagging of the composite comprising the EC-element 608(performing as a substrate), the APBF 602, and the superstrate 620having the coating 630 on its inner surface 624, and (ii) autoclavingthe composite at a temperature within a range from about 80° C. to about110° C. and a gauge pressure of about 100 psi to about 400 psi for atleast 15 minutes. Alternative ranges of processing parameters arediscussed elsewhere in this application. The EC-element was fabricatedaccording to the principles described in U.S. Pat. Nos. 5,818,625 and6,870,656. The suitability of any of the resulting laminate-containingmirror structures for use in the automotive image-preserving reflectorsis demonstrated in FIG. 5, showing a substantially distortion-free imageof the etalon grid formed in reflection 648 of incoming light 650 by theembodiment 600 of FIG. 6. As discussed above, a successful visualevaluation test is defined by an image that is substantially free fromimage distortions. As shown in FIG. 5, the image is continuous acrossthe full FOV of the embodiment 600, the FOV spanning both the displayregion 642 and the outer region(s) 644. In another embodiment, smalldifferences in hue and brightness of the image portions formed by theregions 642 and 644 of the element 600 may be used advantageously toallow easy visual location of the display in the “off” state.

The following examples, described with reference to FIGS. 8(A-J),illustrate advantages of using a reflective polarizer laminated, inaccordance with embodiments of the present invention, within anautomotive rearview mirror assembly that includes a display (an LCD, orotherwise) positioned behind the mirror system. Various datarepresenting optical parameters of the system such as reflectance,transmittance, and absorbance are provided as eye-weighted values (i.e.,for light centered at 550 nm). While the examples of mirror systems andassemblies discussed with reference to FIGS. 8(A, D-G) incorporate anelectrochromic element and an LCD, it is understood that any other typeof automotive mirror element—such as, e.g., a prism mirror element—canbe utilized, and, similarly, that any other suitable type of display maybe used. Discussion of light throughput from a display through aparticular embodiment of the mirror system towards the user assumes theoriginal luminance of the reference display, at the display output, tobe 8,000 cd/m². This value is not limiting but chosen arbitrarily forthe purposes of performance comparison among various embodiments.

FIG. 8(A) shows a prior art embodiment comprising an EC element 800formed by EC-medium secured, within a chamber 614 formed by the firstand second lites of glass (i.e., glass plates) 635 and 610, with aperimeter seal 802 made of a sealant such as epoxy. As shown, anapproximately 145 μm thick ITO coating 817 is applied to the secondsurface (denoted as II, in accordance with the convention defined above)of the first lite of glass 635. The third surface (surface III, of theglass plate 610) is coated with a three-layer coating 804 consisting ofa layer 808 of TiO₂ deposited directly on the second lite 610, an ITOcoating 812 on the TiO₂ layer, and a layer 816 of a metal coatingcomprising an alloy of silver and gold, the concentration of gold beingabout 7 weight-%. Seal 802 may or may not be in physical contact withboth glass plates 610 and 635. As shown, the seal 802 provides a bondbetween the coating 804 and 817. The thicknesses of the coating layers808, 812, and 816 are adjusted to provide for the approximately 55%overall reflectance of the EC element 800. The overall transmittance ofthe EC element 800, measured for unpolarized light, was in the range ofabout 29% to 33%. These reflectance and transmittance levels areselected to provide a generally suitable compromise between the displaylight output, reflectance intensity and ability to make the displaycomponents behind the mirror system to be unperceivable by the observer115. The brightness of an LCD subassembly 639 (emitting light withluminance of about 8,000 cd/m² towards the EC element 800, as shown withan arrow 820) perceived by the observer 115 corresponds to the reducedluminance of about 2,000 cd/m² due to losses upon the propagation of theLCD-generated light 820 through the element 800.

In contradistinction with prior art and in accordance with the presentinvention, an embodiment of a laminate 828 containing a reflectivepolarizer 824 (e.g., an APBF manufactured by 3M, Inc.) may beadvantageously incorporated within a rearview mirror assembly. As nowdescribed in reference to FIG. 8(B), the reflective polarizer 824 waslaminated, according to an embodiment of the method of the invention, toa surface I of a single 1.6 mm thick lite of glass 826. A resultingtransflective laminate 828 was characterized by the overall (unpolarizedlight) reflectance of about 51.1%, and the overall transmittance ofabout 46.5%, with the loss on absorption being about 2.4%. Since theabsorbance of the glass plate 826 was about 0.7%, the absorbance of thereflective polarizer 824 was estimated to be about a 1.7%.

FIG. 9(A) graphically presents a measured spectral dependence of thereflectance of the laminate 828 of FIG. 8(B). For the purposes ofcomparison, optical performance of the embodiment 828 of FIG. 8(B) wasalso calculated with a thin-film design program, using a thin-film stackof 145 alternating layers having refractive indices of 1.35 and 1.55 tosimulate the APBF 824. The thickness of the layers was optimized via aSimplex algorithm so that the reflectance and transmittance matched thevalues measured with embodiment of FIG. 8(B). The values oftransmittance and reflectance calculated based on the human eye'ssensitivity (and generally designated herein by Y), are 46.4% and 51.3%,respectively, demonstrating good agreement with empirical resultsdiscussed above. Specific birefringent properties of the APBF films ofthe embodiments of FIGS. 8(A) through 8(I) were not incorporated in thethin-film design model.

Referring now to the embodiment 830 in FIG. 8(C), the APBF 824 islaminated to two lites of glass, 826 and 832, between surfaces II andIII. The Y reflectance value was within a range of about 48% to about51% and the Y transmittance value is within a range from about 47% toabout 49%. Here, a portion of light 820 penetrating, through the plate826 and the APBF 824, towards the glass plate 832, is reduced due to thehigh value of reflectance of the reflective polarizer 824. In comparisonwith the embodiment 828 of FIG. 8(B), the overall absorption of theembodiment 830 is higher by about 0.4%. The slight reduction ofreflectance figure may be due to either variations in the properties ofthe APBF 824 or, alternatively, due to the change in refractive-indexcontrast at the APBF-surface facing the viewer 115. The modeling of theoptical characteristics of the embodiment 830 resulted in values ofabout 44.1% and about 52.5% for the Y reflectance, the polarizedtransmittance (PT) value of about 89.5%, and transmittance of lighthaving polarization orthogonal to that of the display-generated light ofabout 3.1%. The measured spectrum of overall reflectance of theembodiment 830 in comparison with that of the embodiment 828 of FIG.8(B) is shown in FIG. 9(B) in dashed line.

FIG. 8(D) depicts an embodiment 836 of a rearview mirror assemblycomprising an EC-element 840, which includes the two glass plates 610and 635 that are appropriately overcoated, at surfaces II and III, withITO layers and that form the EC-medium chamber 614, and the embodiment828 of the laminate of FIG. 8(B), bonded to the surface IV of the glassplate 610. During the fabrication process, the EC-chamber 614 is formedby filling the gap between the plates 610 and 635 with an EC-medium andsealing it along the perimeter with an appropriate material such asepoxy. The reflective polarizer 824 is then laminated to the surface IVof the electrochromic element with the addition of a third lite of glass(i.e., plate 826). Alternatively, the reflective polarizer 824 may befirst laminated between the lites 826 and 610, followed by the formationof the EC cavity 614 and the EC-element 840. Alternatively or inaddition, the plate 826 may be made of plastic or other transparentmaterial having suitable optical and physical properties. As described,therefore, the plate 610 may be viewed as a laminate substrate and theplate 826 may be viewed as a laminate superstrate. The overallreflectance and transmittance of this embodiment were measured to bewithin a range of 42% to about 48%, and within a range of about 41% toabout 47%, respectively. In comparison with the above-discussedembodiments 828 and 830, the reflectance values are substantiallyreduced due to the absorption of light in the EC-element 840. Here, theoverall absorbance of the embodiment 836 was about 9% to 11%. In thecase of optimal orientation of the laminate 828 (corresponding to thesituation when the transmission axis of the RP 824 is collinear with thepolarization vector of linearly polarized light 820 generated by the LCD639), the optimal transmittance for polarized light 820 (also referredto herein as the polarized transmittance value, PT) ranges from about75% to about 85%, and that for light having the orthogonal polarizationranges from about 3% to about 5%. When the LCD subassembly 639 producesan output of 8,000 cd/m², the net effective luminance of the displayperceived by the viewer 115 in transmission through the embodiment 836is about 6,720 cd/m². The experimentally measured spectral distributionof the overall (unpolarized light) reflectance of the embodiment 836 isshown in FIG. 9(C) in a solid line, in comparison with that forembodiment 830 of FIG. 8(C), shown in a dashed line. The values ofreflectance and transmittance for the embodiment 836 are about 47.2% andabout 41.5%, respectively. The modeled absorbance is about 11.3%, whichis similar to the experimentally obtained results.

In comparison to the embodiment 836 of FIG. 8(D), the embodiments ofFIGS. 8(E-G) include supplementary coatings, added to increase thereflectance of corresponding mirror assemblies. An embodiment 844 ofFIG. 8(E), for example, includes a bi-layer 846 consisting of a layer ofTiO₂ and an ITO layer deposited, in that order, onto the surface IV ofthe lite of glass 610 prior to laminating the reflective polarizer 824.The bi-layer 846 is designed to be a thin-film structure with apredetermined thickness, e.g., a quarter-wave optical thickness at 550nm. Any measure, taken to modify optical characteristics of the mirrorassembly at the reference wavelength, will affect the visually perceivedperformance of the assembly such as the effective luminance of ambientlight reflected by the mirror assembly to the user 115. The addition ofthe bi-layer 846 increases the overall (unpolarized light) reflectanceto about 48% to 55% and decreases the transmittance to about 33% to 42%,in comparison with the embodiment 836. The transmittance, from thedisplay 639 to the user 115, of light 820 with the preferredpolarization is about 68% to 76% and that of light with orthogonalpolarization is about 3% to 5%. The net throughput of thedisplay-generate light through the embodiment 844 is about 5,930 cd/m²,

Comparing now the embodiment 850 of FIG. 8(F) to the embodiment 844 ofFIG. 8(E), in the former the TiO₂/ITO bi-layer 846 is deposited on thesurface V of the glass plate 826 prior to the lamination of the RP 824between the glass plates 826 and 610. As a result, the overallreflectance of the assembly 850 is about 48% to 55%, which is similar tothe reflectance of the embodiment 844 of FIG. 8(E). The overall(unpolarized light) transmittance, however, is decreased to about 33% to42%. The transmittance value obtained for light of optimal polarizationis about 68% to 76%, while that for light having an orthogonalpolarization is about 3% to 5%. The net luminance, of thedisplay-generated light, perceived by the user 115 through theembodiment 850, is about 5,460 cd/m². It appears, therefore, that incomparison with the embodiment 850, the major effect produced byreversing the order of the bi-layer 846 and the APBF 824 is the slightdifference in the optimal transmittance of light having preferredpolarization. This may be due to either the experimental variability inthe measurement process or variations in the materials used inconstructing the optical system.

In the embodiment 860 of FIG. 8(G), the TiO₂/ITO bi-layer 846 isdisposed on surface VI of the glass plate 826. Such positioning of thelayer 846 results in the overall (unpolarized light) reflectance ofabout 55.1%, while the overall (unpolarized light) transmittance isabout 31.4%. The transmittance of light having the optimal polarization(i.e. polarized transmittance value, PT) is about 59.6% while thetransmittance of light with the orthogonal polarization is 3.1%. The netthroughput of the display light 820 through the embodiment 860 is about4,770 cd/m². Comparison of the experimentally determined spectra forreflectance of the unpolarized light for embodiments of FIGS. 8(D-G) ispresented in FIG. 9(D).

In another embodiment of the invention, shown in FIG. 8(H) in anexploded view, the APBF 824 is laminated between the plate 826 and theEC-element 877, which are all disposed in front of the LCD 639 and alight engine 870. As shown, a conventional LCD 639 includes an LC medium872 sandwiched between two polarizers, 874 and 876. Optimization oflight transmission from the light engine 870 through the LCD 639 throughthe laminate 828 towards the EC-mirror system 877 may be achieved byorienting the APBF 824 so as to have its transmission axis 878 to becollinear with the transmission axis 880 of the front polarizer 876 ofthe LCD. The transmission axis of the back polarizer 874 of the LCD isdenoted as 882. (Optionally, the orientation of the polarizer 874 in thexy-plane may be changed if desired so as to rotate the axis 882 by apredetermined angle, e.g., ninety degrees, to change the display modefrom “bright” to “dark.”) In this maximum transmission orientation, theRP 824 transmits approximately 88.5% of polarized light 820 emanatingfrom the LCD 639 generally in +z direction and reflects about 50% of theunpolarized ambient light (not shown) incident upon the laminate throughthe EC-element 877 back to the viewer 115 (not shown). In this case, thebrightness of the LCD subassembly 639 having luminance of 8,000 cd/m²would be perceived by the viewer 115 as corresponding to about 7,080cd/m². In a minimum transmission orientation of the RP 824(corresponding to a setting in which the transmission axes 878 and 880are substantially perpendicular, not shown) the transmission of lightfrom the LCD 639 to the viewer 115 drops to about 3.8%. Incontradistinction, the polarization-insensitive transflective elementsof prior art, such as those comprising the embodiment of FIG. 8(A),would not be capable of simultaneously attaining the 88% transmittanceand 50% reflectance. It is worth noting that, generally, a frontpolarizer 876 of the LCD 639 can be removed, in which case the properlyoriented RP 824 can operate as the front polarizer of the LCD. In anembodiment of a display employing the absorptive polarizer. the RP maybe used instead of the absorptive polarizer. In this case, theextinction ratio, i.e., the ratio of intensities of light with twoorthogonal polarizations, will affect the effective contrast ratio ofthe display. Preferably, the transmittance of the off-axis polarizationstate (the polarization state when the LCD is in the off position)should be less than 5%, preferably less than 2.5%, more preferably lessthan 1% and most preferably less than 0.5%. The lower transmittancevalues of the off-axis polarization state leads to images with darker“black” parts of the image.

The effect produced by a reflectance-enhancing coating on the overall(unpolarized light) reflectance and polarized transmittancecharacteristics of a mirror assembly may be quantified by defining afigure of merit such as, e.g., the ratio of the polarized transmittanceand the overall reflectance (PT/R). This figure of merit is listed inTable 3, together with the corresponding reflectance and transmittancedata discussed above with reference to embodiments of FIGS. 8(A-G). Inaddition, Table 3 contains the data representing performancecharacteristics associated with an embodiment similar to the embodiment836 of FIG. 8(D) but having the lite 826 removed. FIG. 10 presents thedata of Table 3 in a graphical form. In an attempt to optimize thestructure of an automotive mirror assembly (that comprises anAPBF-laminate and has a given overall, unpolarized light reflectancevalue) by achieving high polarized transmittance, variousreflectance-enhancing layers may be evaluated and those providing forhigher polarized-transmittance-to-overall-reflectance (PT/R) ratios maybe preferred. The choice of materials for an APBF may also be based onsimilar criteria. For example, in comparison with the PT/R ratio of 0.45for the prior art transflective mirror assembly embodiment 800, the PT/Rratio of the embodiments of the current invention (where the employedthin-films stacks may or may not include the reflectance-enhancinglayers) may be increased above 0.5 and preferably above 0.75. In aspecific embodiment, the PT/R ratio may be increased to above 1.0 andpreferably above 1.25.

TABLE 3 Light Increase of Throughput, PT, [times] Overall Overall[cd/m²] (in Reflectance Transmittance (from comparison R, [%] T, [%]Polarized Display of with (unpolarized (unpolarized Transmittance 8,000cd/m² embodiment Embodiment light) light) PT, [%] to Viewer) 800) PT/R800, FIG. 8(A) 55.0 25.0 25.0 2,000 1.0 0.45 828, FIG. 8(B) 51.1 46.588.5 7,080 3.5 1.73 830, FIG. 8(C) 50.2 47 89.5 7,163 3.6 1.78 836, FIG.8(D) 45.3 44 84.0 6,719 3.4 1.85 836 (with 45.6 43.3 81.8 6,542 3.3 1.79superstrate 826 removed) 844, FIG. 8(E) 50.6 37.5 74.2 5,933 3.0 1.47850, FIG. 8(F) 50.6 36.7 68.3 5,463 2.7 1.35 860, FIG. 8(G) 55.1 31.459.6 4,766 2.4 1.08

For example, applying quarter-wave dielectric coatings to at least oneof surfaces I and II in a mirror assembly embodiment that comprises anEC-element and a reflective polarizer (such as embodiments of FIG. 6 orFIG. 8(D)), potentially increase the overall reflectance of the mirror.The gain in reflectance, however, may come at the expense of somedisadvantages such as spurious reflections perceived as double-imagesand higher reflectance of the rearview mirror system in the “darkened”state. The “darkened state corresponds to the situation when thetransmittance of the EC-element is minimized and interfaces behind theEC-medium do not meaningfully contribute to the overall reflectivity ofthe mirror assembly. Therefore, in one embodiment it may be preferred tohave surfaces I and II with low reflectivity values. If the reflectivityof at least one of surfaces I and II is minimized, then in the darkenedstate the overall reflectivity of the described mirror assembly is alsominimized as the overall reflectivity is predominantly defined, in thedarkened state, by reflectance values of surfaces I and II. As a result,the dynamic range of the reflectance of the mirror assembly may bebroadened. The reflectivity of surface II may be reduced, for example,by depositing a half-wave thin-film layer on surface II. On the otherhand, in another embodiment, it may be desirable to increase the valueof overall reflectance that the mirror has in the darkened state. Forexample, some automotive manufacturers prefer that the minimumreflectance of convex or aspheric outside EC-mirrors be above twelvepercent. An appropriate adjustment of the overall minimum reflectancevalue can be achieved by disposing a reflectance-enhancing coating infront of the EC-layer (with respect to the viewer), e.g., on surface Ior surface II, instead of disposing such a coating behind the EC-layer.Other methods such as adjusting the cell spacing of the EC-element orthe concentrations of the anode and cathode materials, or the variationof the operating voltage may also be used to adjust the minimumreflectance of the device.

The reflectance of a surface overcoated with a single dielectricoverlayer can also be enhanced by adding a pair of layers to the singledielectric overlayer. The refractive index of one such layer, designatedas low (or L), should be smaller than the refractive index of the singledielectric overlayer, while the index of the second layer, designatedhigh (or H), should be larger than the refractive index of the L layer.The H layer may be made of the same material as the single dielectricoverlayer, or it may be made of a different material. The degree towhich the overall reflectance of an optical surface is enhanced dependson the index contrast of the thin-film materials used for suchenhancement. The equivalent optical thickness of each of the H and Llayers in the enhancing pair of layers should be about a quarter-wave soas to maximize the resulting reflectance of the thin-film stack.Preferably, in such a pair of layers, the refractive index of thereflectance-enhancing layer with the “high index” value is greater thanabout 1.7, and more preferably greater than 2.0. In some embodiments,such index may be on the order of or even exceed 2.4. Preferably, thedifference between indices of the H and L layers should be greater thanabout 0.4 and more preferably greater than about 0.7. In someembodiments, the index of L-layer may be more than 1.0 below that ofH-layer. Additional high/low pairs can be added to further enhance thereflectance. For instance, the overall material stack may comprise(starting with materials farthest from viewer) G/RP/H/G.

Alternative embodiments of the structures having enhanced reflectance,for use in automotive mirror assemblies may be, e.g., G/RP/H/L/H/G, orG/RP/H/L/H/G/ITO/EC/ITO/G and similar structures, where, instead of alayer of the ITO on surface III, a semi-transparent layer of metal(preferably Ag or Ag-based alloy such as silver-gold alloy, which isknown to be chemically stable when in contact with most fluid-based ECmedia) may be used for enhancement of reflectance. Additional layers maybe employed to attain color neutrality in reflection, as discussed invarious commonly-assigned patent applications. In the abovementionedstructures, G denotes a glass layer (substrate); RP corresponds to areflective polarizer component; H and L conventionally denote dielectriclayers with high and low refractive indices, respectively; and ECsymbolizes a layer of electrochromic medium. The H and L layers or anycombination of such layers may be deposited directly onto the glasssubstrate or, alternatively, may be disposed directly onto thereflective polarizer component, depending on the requirements of a givenapplication. The refractive index of any bulk layer interface in thereflective polarizer system can also play a role in modifying,attenuating or enhancing the reflectance. In general, to enhancereflectance a larger difference in refractive index between twoneighboring materials is preferred. Conversely, minimizing thedifference in the refractive index between neighboring materialstypically will reduce the reflectance. Any additional interfacematerials present on the reflective polarizer can influence thereflectance due to the refractive index mismatch phenomena.

If an additional depolarizer (in the form of a depolarizing layer, forexample), or pressure sensitive adhesive or other material is placedbetween the reflective polarizer and a coated or uncoated glass surfacethen the refractive index of this material will be a determining factorin the final reflectance. For example, in one embodiment, when ahigh-index reflectance-enhancing layer is present on surface IV of thesystem, the system reflectance may be maximized if the neighboringmaterial has a relatively low refractive index—the lower the better. Itis understood that optimization of the entire system is required toachieve a desired set of properties. The optimal refractive indices ofmaterials used will generally depend on the indices of surroundingmaterials and may vary depending on the application.

In other possible embodiments, as discussed below, the use of a gradedindex material between the reflective polarizer and the adjacent glasssurface may result in the optimal reflectance effects if the there aredivergent requirements for the reflective polarizer and the coated oruncoated neighboring surface or interface. Non-limiting examples ofsuitable high refractive index layers are: antimony trioxide, cadmiumsulfide, cerium oxide, tin oxide, zinc oxide, titanium dioxide orvarious titanium oxides, lanthanum oxide, lead chloride, praseodymiumoxide, scandium oxide, silicon, tantalum pentoxide, thallium chloride,thorium oxide, yttrium oxide, zinc sulfide, zirconium oxide, zinc tinoxide, silicon nitride, indium oxide, molybdenum oxide, tungsten oxide,vanadium oxide, barium titanate, halfnium oxide, niobium oxide, andstrontium titanate. Non-limiting examples of suitable low refractiveindex layers are: aluminum fluoride, aluminum oxide, silicon oxide,silicon dioxide, calcium fluoride, cerium fluoride, lanthanum fluoride,lead fluoride, lithium fluoride, magnesium fluoride, magnesium oxide,neodymium fluoride, sodium fluoride, thorium fluoride or a porous filmwith high density of voids. The reflectance value of the mirror systemand spectral properties of light reflected by the system can be furthertuned by using at least one optical layer having material propertiesthat vary with layer thickness. A common example of such materiallynon-uniform layer is known as a graded composition coating (GCC). Incomparison with the graded thickness layers (characterized by spatiallyuniform material properties and spatially non-uniform thickness), a GCCmay have a spatially non-uniform material composition resulting, e.g.,in a refractive index that varies as a function of thickness. In oneembodiment, the mirror assembly may include a GCC formed with a variablemixture of SiO₂ (refractive index of about 1.45) and TiO₂ (refractiveindex of about 2.4). For example, next to a substrate onto which the GCCis deposited, the GCC may predominantly contain SiO₂ (and, therefore,have a refractive index approaching 1.45). Throughout the thickness ofthe GCC, the material composition of the GCC is varied to increase thecontent of TiO₂. As a result, the refractive index of the outer portionof the GCC may be approaching 2.4.

Alternatively or in addition, the overall reflectance of the rearviewmirror assembly containing a multi-layered RP may be increased byaltering the layers of the RP component. This may be accomplished, e.g.,by adjusting thicknesses of different layers in the reflectivepolarizer. Alternately, the indices of these layers may be altered. Thenet reflectance and transmittance may thus be adjusted or tuned to theneeds of a given application. In an typical inside rearview automotivemirror the reflectance is preferably greater than about 45%, morepreferably greater than 55%, even more preferably greater than 60% andmost preferably greater than about 65%.

The spectrum of light reflected (and, therefore, transmitted) by anembodiment of the mirror system of the invention can be tuned byadjusting the thickness of the reflectance-enhancing layers. The peakreflectance will vary with optical design wavelength and this willresult in a change in the reflected (and transmitted) color. Colordistribution may be characterized according to the CIELAB color systemand the L*a*b* color quantification scheme. The color values describedherein are based on the CIE Standard D65 illuminant and the 10-degreeobserver. According to the scheme, L* represents the brightness of theobject and Y, as used in this application, represents the overallreflectance, a* defines the green and red color (positive) components,and b* defines blue and yellow color (positive) components. Table 4illustrates the calculated changes in spectral distribution of lightreflected by the embodiment of FIG. 8(D) in which a single layer oftitania, TiO₂, has been additionally disposed on surface IV. In thiscalculation it was assumed that the refractive index of TiO₂ layerequals n=2.24 (with recognition that in practice this index may somewhatvary due to processing conditions). In comparison, Table 5 similarlyillustrates changes in spectral distribution of ambient light reflectedby the embodiment of FIG. 8(D) in which an H/L/H stack has beenadditionally deposited on surface IV. In this calculation it is assumedthat the high index layer has a refractive index of 2.24 and the lowindex layer has a refractive index of 1.45. The thin film modelsdescribed above were used for both of these calculations. The designwavelengths, in Tables 4 and 5, are the same and in each case allquarter-wave layer thicknesses are adjusted to the same designwavelength. As shown in Table 4, the reflectance reaches its peak valueat a design wavelength of about 550 nm. The color gamut of the reflectedlight shifts towards blue (which is indicated by lower values of b*)when the design wavelength drops below approximately 450 nm, and towardsyellow/red for design wavelengths of about 500 nm and above (which isindicated by increase of b* and a*). This effect is achieved due topreferential enhancement of the reflectance of the assembly in certainportions of the visible spectrum. As can be seen from comparison ofTable 4 and 5, the additional layers magnify the changes in spectraldistribution of reflectance, which is indicated by variations of a* andb* increasing with changes to the optical thickness of the stack.Appropriate adjustment of optical thicknesses, refractive indices,and/or the number of layers in the stack independently may lead to aparticular spectral distribution of reflectance, as may be required by aspecific application of the mirror assembly. For instance, a givenreflectance with a yellow hue may be obtained or a different reflectancewith a blue or red hue may be obtained by the appropriate tuning of thelayer thicknesses.

TABLE 4 Reference Wavelength, nm Cap Y a* b* RP alone 47.18 2.95 −3.61400 49.43 2.03 −3.8 450 49.78 1.88 −3.57 500 49.97 1.81 −3.26 550 50 1.8−2.91 600 49.9 1.87 −2.56 650 49.67 2.02 −2.27 700 49.35 2.25 −2.1 75048.96 2.55 −2.1

TABLE 5 Reference Wavelength, nm Cap Y a* b* RP alone 47.18 2.95 −3.61400 51.79 0.51 −7.51 450 55.13 −1.47 −5.46 500 57.36 −2.36 −2.16 55057.91 −2.12 1.42 600 56.78 −0.5 3.74 650 54.41 2.37 3.32 700 51.62 50.85 750 49.35 5.71 −1.56

Adjustment of the overall reflectance in embodiments of the presentinvention may be carried out by employing laminates containing more thanone APBF elements. For example, embodiments of laminates of theinvention characterized in Table 6 were structured as[Glass/RP/RP/Glass]. FIG. 25 schematically illustrates this structure inexploded view, where two DBEF-Q films 2510, 2520 used as RPs aresandwiched between the glass substrates 2530, 2540. The APBF 2510 isoriented so as to have its polarization axis 2530 be collinear with thepolarization of the LCD (not shown) output, indicated in the table as“s-pol’ which corresponds to the x-axis. Polarization axis 2560 of theadjacent DBEF-Q film 2520 is rotated with respect to the axis 2530 in anxy-plane, which is parallel to the films, by an amount indicated in thecolumn “Trial”. The data of Table 6 are shown for a D65 illuminant 10degree observer. Unless indicated otherwise, the data are notpolarization specific. The measurement data demonstrates that, bycombining a plurality of angularly misaligned reflective polarizers inan embodiment of the invention, a decrease in transmission of light fromthe display may be traded-off for an increase in the overall reflectanceof the embodiment. It shall be realized that, in practice, additionaloptical layers may be disposed adjacent to at least one of the pluralityof APBFs. Some embodiments employing a plurality of APBFs, such as thosedescribed in Table 6 or the like, may require that light transmittedfrom the display to the observer be color neutral. This situation mayarise in embodiments employing a reverse camera display (RCD). Therequired color neutrality may be achieved by adjusting a displayalgorithm for more accurate color rendering. In some embodiments, theadjustments of the display algorithm may allow for compensation of thecolor induced transmission bias from electrochromic medium or othercomponents.

Some applications may require a neutral spectral distribution ofreflectance figure of the mirror assembly (such distribution may, forexample, lack high purity hues). The magnitude of the color, or C*, maybe defined as

Color Magnitude=C*=√{square root over ((a*)²+(b*)²)}{square root over((a*)²+(b*)²)}

In one embodiment of the current invention the color magnitude may besmaller than about 15. In a related embodiment, the color magnitude maybe smaller than about 10, and, in a specific embodiment, it may be mostpreferably less than about 5.

TABLE 6 Figure Transmittance of In Reflection In Transmission % Merit,Trial Y a* b* Y a* b* Absorbance % p-pol s-pol PT/R  0 51.38 −0.52 −0.3945.7 −0.23 1.68 2.95 0.85 88.95 1.73 deg 15 55.99 −0.84 −0.96 42.9 0.052.29 1.07 1.42 76.96 1.37 deg 30 59.81 −0.73 −1.02 39.6 −0.04 2.57 0.612.31 71.64 1.20 deg 45 65.33 −1.29 −1.52 33.1 0.84 3.43 1.62 2.73 52.360.80 deg 60 74.91 −1.20 −1.50 20.4 1.30 5.70 4.66 4.17 31.00 0.41 deg 7584.11 −2.40 −2.29 11.1 6.99 13.20 4.78 5.15 8.20 0.10 deg 90 88.53 −1.95−2.16 6.3 8.43 22.56 5.21 5.91 5.57 0.06 deg

In some embodiments, the area of the display may be smaller than thearea of the mirror element. Such embodiments are illustrated, forexample, in FIGS. 8 (A, C—F, H) or in FIG. 6. The relatively hightransmittance of the reflective polarizer would generally make othercomponents in the mirror assembly to be visible to the viewer. Topreserve high polarized transmittance values of the RP component whilesimultaneously concealing these other components in the system (e.g., inthe outer areas 644 of FIG. 6), opacification may be employed. Practicalmeans of such opacification may include, but not be limited to, additionof an opaque material such as of plastic, or a layer of paint or ink, ora thin-film coating, suitably applied to an element of the mirrorassembly, across a rearward surface of the system relative to thereflective polarizer. Depending on an embodiment of the EC-mirrorassembly, such opacification may be carried out on surfaces III, IV, Vor VI. In embodiments containing a prism-based mirror (such as, e.g.,embodiments of FIGS. 4(B-D), 4(F) and 4(G)), the opacification may becarried out on surfaces II, III, or IV. Although embodiments of thepresent invention describe specific mirror systems having up to 3 litesof glass (or other material), additional lites may be used withoutlimitation as needed to meet requirements for the system. If additionallites are employed, an opacification layer may be placed on one or moreappropriate surfaces located behind the reflective polarizer relative tothe viewer, which may result is aesthetically pleasing appearance of theoverall rearview mirror assembly. The opacification means could bepresent across the entire area outside of the display or only inselected locations, as needed.

In addition, as discussed below, in a specific embodiment of theinvention, at least some edges of the opacified areas around theperimeter of the display region may be formatted to gradually vary thetransmittance of the mirror across its surface from fully transparent tofully opaque (and to accordingly gradually vary the reflectance of themirror across its surface). Literature provides some solutions foraesthetic gradual transitions from a display area to adjacent areas havebeen discussed in the literature. For example, in the area of therearview automotive mirrors the need for good match in color andreflectance has been recognized and thin-film coating-based solutionshave been proposed in, e.g., commonly assigned U.S. patent applicationSer. Nos. 11/713,849, 12/138,206, and 12/370,909, the disclosure of eachof which is incorporated herein by reference in its entirety. Agraded-thickness coating has been used in front of an APBF in, e.g.,U.S. Patent Publication 2006/0164725 as a means of gradual variation ofreflectance across the surface of a conventional viewing mirroremploying a display. The same publication discussed additional means ofhiding the edges of the display area in conventional viewing mirrors byadding a supplementary coated substrate, having a relatively highreflectance and low transmittance, in front of the APBF. Although thissolution facilitates concealing the edges of the display area, itsuffers from the effect of parallax, whereby the spurious images areformed in reflection from the viewing mirror. Additional disadvantagesof this solution stem from reduction in brightness and contrast of thedisplay, now perceived by the viewer through the viewing mirror and thesupplementary substrate. Overall, the proposed solutions were recognizedto be inapplicable to the field of automotive mirrors. The trade-offbetween a clearly discernable edge of the aperture or a parallaxcondition is generally recognized and no viable solution which avoidsparallax and has a stealthy edge at the display area of the mirror hasbeen realized so far. Other prior art means to adjust the reflectance(such as changing the density of reflective particles contained within acoating placed in front of the RP included in the mirror system) mayresult in varying haze levels (scattering from agglomerated particleswithin the coating) and make the edges of the aperture noticeable. In anembodiment of the present invention, the reflectance may be varied fromspecular to non-specular or the intensity of light reflected from themirror may be varied or graded along the edge of the opacified area. Inan embodiment of the APBF-containing rearview mirror of the presentinvention, depending on the size and location of the display, it may bepreferred to grade either some or all of the edges of the opacifiedareas around the display region. The required gradations oftransmittance or reflectance may be implemented by, for example, eitherspatially modifying the transmittance of the opacifying material itselfor by patterning such material in a spatially non-uniform fashion. Suchgradations may be implemented in various ways such as those described ina commonly assigned U.S. patent application Ser. No. 12/370,909. In aspecific embodiment such pattern may comprise, for example, a pattern ofdots created with varying spatial density. FIGS. 17(A) and 17(B)demonstrate front views of opacifying layers with graded edges formattedin tapered and feathered fashions, respectively.

Structurally, embodiments of the mirror system of the inventioncontaining graded-thickness opacifying layers may differ. For example,in an exemplary EC-type embodiment 884 of the invention, schematicallyshown in FIG. 8(I), a mirror system may be structured similarly to thatof FIG. 8(F) but additionally have a graded-thickness opacifying layer886 made of metal (such as Cr, Al, Ag or Ag alloy, Rh, Pd, Au, Ru,Stainless Steel, Pt, Ir, Mo, W, Ti, Cd, Co, Cu, Fe, Mg, Os, Sn, W, Zn oralloys, mixtures or combinations of the above) that is disposed onsurface V of the mirror system. It would be realized that, generally,the reflectance-enhancement layer 846 added between the surface V andthe graded-thickness opacifying layer 886, is optional. In a specificembodiment, the reflectance-enhancement layer 846 may include an oddnumber of quarter-wave thin-film layers, e.g. a single layer or aquarter-wave stack such as H/L/H stack (TiO₂/SiO₂/TiO₂, for instance).As shown, all the perimeter of a window 888 in the layer 886 has gradededges. The thickness of the layer 886 varies across the plane of themirror (i.e., in xy-plane) between essentially zero and the maximumthickness (e.g., 500 Å). For comparison, FIG. 17(C) shows a front viewof another embodiment 1710 of a graded opacifying layer that is limitedwith graded edges only along the length of the mirror (x-axis, asshown). In a second dimension (y-axis), a window 1720 in the gradedlayer 1710 extends to the very edge of the mirror itself Grading of thethickness of opacifying layer 1710 along the length of the mirror, asmeasured, is clearly seen from FIG. 17(D). The purpose of grading ththickness of the edges is to make the transition between the display andopaque regions less noticeable to the viewer. Such gradual opacificationor reflectance modification approaches may allow one to minimize thevisibility of the features behind the mirror in diffuse lightingconditions. This approach thus improves the aesthetics of the mirrorassembly regardless of whether a laminate, comprising a reflectivepolarizer such as the APBF, is a part of such assembly or not, and it isapplicable in various other types of mirrors (e.g., electrochromic,simple reflectors such as or simple tilt-prism mirrors, or other mirrorssuitable for use in automotive applications). Positioning of theopacifying layer, such as the layer 886, behind the RP 824 in anembodiment of the rearview mirror of the present invention facilitates asolution of problems acknowledged in prior art. In particular, suchorientation of the components in the mirror system allows for reductionof the visibility of the edges of the opening 888 in the graded-edgeopacifying layer without either the accompanying parallax effect orreduction in brightness and contrast of the display observed by theviewer 115.

Generally, a means for opacification and a means for reflectanceenhancement may be combined or used alternatively in the areas of themirror assembly outside the display area (such as areas 644 of FIG. 6representing mirror areas outside of the display area 642) to reducevisibility of components located in those areas behind the mirror whilesimultaneously increasing the reflectivity. The value of transmittancein such outer areas 644 should be reduced, by either opacification, orenhancement of reflectance, or combination of both, to levels lower thanabout 10% and preferably lower than about 5%. In other embodiments, suchtransmittance may be reduced to levels lower than about 2.5% or evenlower than about 1%. Various surfaces of the mirror assembly can betreated to simultaneously achieve the opacification andreflectance-enhancing effects, depending on the requirements of a givenapplication. For instance, in an embodiment comprising an EC element infront of the reflective polarizer (as viewed by the observer, such as,e.g. in the embodiment of FIG. 8(D)), a layer having both the opacifyingand reflectance-enhancement properties, further referred to herein asthe opaque reflectance-enhancing layer (OREL), may be disposed onsurfaces III, IV, V, or VI. In a related embodiment, without the ECdevice, comprising a reflective polarizer between the two lites of glass(such as the embodiments of FIG. 4(C) or 8(C), for instance), one ofwhich may be a prism, the OREL could be placed on surfaces I, II, III,or IV. Generally, in an embodiment where the OREL is disposed behind theRP (e.g., close to surface V of FIG. 8(I)), it increases the reflectanceof the reflective polarizer element and lowers the transmittance of themirror system beyond the increase of reflectance of the RP. Incomparison, in an embodiment where the OREL is disposed in front of theRP, as viewed by the observer, it will provide a dominating contributionto the overall system reflectance, which can be calculated usingstandard thin-film modeling techniques. Transmittance of an OREL ispreferably sufficiently low to attain the transmittance targets for thesystem defined above (i.e., concealing components located behind themirror assembly) while in some embodiments simultaneously increasing thereflectance. Requirements imposed on an OREL differ from those for thereflectance-enhancing layers described above that are used foroptimization of optical performance of the display area of the mirrorsystem. In particular, the reflectance-enhancing layers in the displayarea are selected and positioned so as to simultaneously optimize thereflectance and transmittance of a portion of the mirror assembly thatis optically coupled with the display area. (The efficiency of suchperformance enhancement was described using the PT/R ratio, in Table 3,for example). In the areas outside of the display, however, there is noneed to preserve the polarized transmittance and other materials may beused to obtain enhanced reflectance and opacification. Suitablematerials include, but are not limited to, metals, borides, nitrides,carbides, sulfides, and combinations of these materials.

Both the overall (unpolarized light) reflectance of the mirror assemblyand the reflectance of light having a particular polarization depend ona material structure of the assembly. A description of a materialstructure of a mirror assembly can be provided, e.g., by listingmaterial components of such a structure in the order starting from acomponent that is distal to the viewer towards a component that isproximal to the viewer. A structure of the embodiment 830 of FIG. 8(C)can be described as [G/RP/G] (where G, RP, and G respectivelycorresponding to components 826, 824, and 832), while a structure of theembodiment 836 of FIG. 8(D) can be similarly described as[G/RP/G/ITO/EC/ITO/G] (where the listed components respectivelycorrespond to components 826, 824, 610, 808, 614, 817, and 635).

FIG. 11 illustrates the depolarizing effect of an OREL on performance ofthose areas of the mirror structure that are located outside of thedisplay area. FIG. 11 schematically shows a section 1100, of anembodiment of the mirror system, corresponding to one of the areas 644of FIG. 6. The section 1100 includes a front portion 1110, defined as aportion of the mirror system located between the viewer 115 and anelement disposed behind the RP 824, and an OREL 1120 that is opticallyconnected to the front portion 1110 through an optional adjacent medium1130. In practice, the adjacent medium 1130 when present may includeair, polymer, adhesive, or other medium. The OREL may be directlydeposited onto the RP or, alternatively, it may be deposited on anadditional lite of glass that is further bonded to the RP. By way ofexample, a front portion of the embodiment of FIG. 8(D) would includethe EC element 840 and the reflective polarizer 824 portion of thelaminate 828. A corresponding front portion of the embodiment of FIG.8(E) would contain the EC element 840, the bi-layer 846, and thereflective polarizer 824. Referring again to FIG. 11, a portion 1140 ofincident ambient light 1150 having a first polarization that ispredominantly transmitted by the RP 824 will pass through the frontportion 1110 of the mirror system and the optional adjacent medium 1130and will be reflected by the OREL 1120 back towards the viewer 115, asindicated by an arrow 1155. A complementary portion 1160 of ambientlight 1150, having a second polarization that is opposite the firstpolarization, is substantially reflected by the RP 824 towards theviewer 115 and combines with the beam 1155. When the two reflected beams1155 and 1160 having opposite polarizations are combined, a degree ofpolarization of the overall reflected beam 1170 is not as high as itcould be otherwise. The use of an OREL in some embodiments of thepresent invention, therefore, allows for a less-polarized reflection oflight from the mirror assembly towards the viewer and simultaneousincrease in the overall reflectance of the assembly. The use of ORELserves to effectively depolarize the light. A degree of lightdepolarization can be varied by appropriately selecting materials forOREL and adjacent media separating the OREL and RP.

Referring again to FIG. 11, multiple reflections within the mirrorassembly may be taken into account. The amount of net reflectance 1180can be calculated, as is well known in the art, based on the indexdifferences at the interfaces within the mirror assembly, the values ofabsorbance and thicknesses of the materials involved, and the value oftransmittance of the reflective polarizer averaged over twopolarizations (the preferred polarization of light generated by thedisplay and the one orthogonal to it). By way of example, in aparticular embodiment the front portion of the mirror assembly,including the reflective polarizer, reflects unpolarized light with44.5% efficiency, transmits light of preferred polarization withefficiency of 81.8%, and transmits only 3.0% of light having orthogonalpolarization. An OREL with a reflectance of 70% in air as adjacentmedium, as shown in FIG. 13, will result in the net added reflectance of[0.818*0.7*0.818+0.03*0.70*0.03]*0.5=0.2345, or 23.45% In such a case,the overall reflectance of the embodiment of FIG. 11 would be the sum of44.5% and 23.45%, or about 68%. Reflectance properties of the ORELdepend, in part, on the refractive index of the adjacent medium 1130.For instance, the reflectance of a metal surface in contact withdielectric material is reduced as the refractive index of suchdielectric material is increased. Reflectance of OREL including achromium/ruthenium bi-layer (500 Å of chromium and 200 Å of ruthenium)in air as the adjacent medium 1130, e.g., may be about 70%. However, thereflectance of the same bi-layer OREL with a dielectric adjacent mediumhaving an index of 1.51 will reach only about 58.5%.

Table 7 shows experimentally determined reflectance andcolor-qualification parameters associated with various embodiments ofthe invention. In the following, Samples 1 through 7 are located in air(i.e., air is the incident medium). Sample 1, representing a simplemirror formed by an approximately 500 Å thick single layer of chromiumon a glass substrate, has a reflectance of 57%. Sample 2 represents alaminate including a reflective polarizer (DBEF-Q film) laminated tosurface IV of an EC-element (with ITO coatings on surfaces II and III)according to the method of the invention, and corresponds to theembodiment 836 of FIG. 8(D) with the lite 826 removed. Sample 2 reflectsabout 44.4% of the unpolarized light. Sample 3 represents a combinationof the sample 1 disposed behind the sample 2 and separated from it by anair gap. The overall reflectance of Sample 3 is about 66%. Sample 4represents the embodiment 836 of FIG. 8(D). As can be seen from thecomparison of optical characteristics of Samples 3 and 4, the additionof the third lite of glass 826 does not appreciably affect thereflectance of the mirror assembly. Sample 5 is constructed bypositioning Sample 1 behind Sample 4 and separating them with anair-gap. Sample 5 has a reflectance value comparable to that of Sample3. Sample 6 represents a bi-layer coating (including an approximately500 Å thick chromium layer and an approximately 200 Å thick rutheniumlayer deposited on glass in that order. The reflectance of sample 6 ismeasured in air (air is the adjacent incident medium) and equals about69.8%. Sample 7 describes the embodiment where sample 6 is behind sample2 with an air gap. The reflectance is increased from about 44% to morethan 71%. As noted above, the refractive index of the incident mediumadjacent a metallic layer affects the reflectance of the metallic layer.The index-matching oil, used instead of air as incident medium withSamples 8 and 9, has a refractive index of approximately 1.5, and isused to suitably simulate laminations with materials such glass orplastics with similar refractive indices. In these examples, the use ofthe index-matching oil is optically comparable to having the coatedglass laminated to the mirror assembly on the rearward surface. Asdescribed above, the reflectance of a metal coating is decreased whenthe index of the adjacent medium is higher than 1. The index-matchingoil or laminate has a refractive index of about 1.5 and thus lowers thereflectance values of Samples 8 and 9 in comparison with Sample 7.

Sample 6, discussed in reference to Table 7 and having achromium/ruthenium bi-layer, demonstrates spectrally neutral reflectance(with a* and b* values near zero). Other metals or compoundscontemplated in this embodiment may be used to provide opacification,reflectance enhancement and/or color tuning. Different metals andcompounds may have different reflected colors and can therefore be usedto tune the color of the coating stack in the region outside the displayarea as taught, for example, in U.S. patent application Ser. Nos.11/833,701 and 12/370,909, incorporated herein in their entirety byreference.

TABLE 7 Sample Description of # Embodiment R a* b* 1 Mirror with R = 57%57.0 −1.1 1.5 2 An EC-element with ITO 44.4 −2.1 2.4 coatings onsurfaces II and III and APBF laminated to surface IV 3 Sample 1positioned behind 65.8 −3.7 1.90 sample 2, with air gap in between 4 AnAPBF laminated 44.7 −2.0 −2.5 between the EC-element (comprising ITOcoatings on surfaces II and III) and third lite of glass (see embodiment836 of FIG. 8(D) 5 Sample 1 positioned behind 65.9 −3.0 1.9 sample 4,with air gap in between 6 Chromium/Ruthenium bi- 69.8 0.0 0.1 layer onglass substrate 7 Sample 6 positioned behind 71.4 −3.5 1.6 the APBF ofsample 2, with bi-layer facing APBF and separated from APBF by air- gap8 Sample 6 adjacent to sample 66.8 −3.5 1.6 4 with index-matching oilbetween bi-layer and APBF 9 Sample 6 adjacent to sample 66.5 −3.4 1.6 2with index-matching oil between bi-layer and APBF

By analogy with graded opacifying layers discussed in reference to FIG.17, an OREL layer (assuring both the opacification andreflectance-enhancement effects, as discussed above) may also exhibit agraded transition between the display area and the adjacent opaque area.In one embodiment, the OREL is located behind the RP, is absent (haszero effective thickness) in the area of the display and graduallyincreases its thickness (and, therefore, reflectivity) across thesurface towards the “opaque” region. Optionally, a thin transflectivelayer (e.g., an OREL layer or another transflective layer) with finitethickness may be present at the display area to facilitate adhesionand/or optimize aesthetic appearance of the rearview mirror. The gradualtransition of the OREL layer would achieve the effect of concealing atleast one edge of the display area. In addition, the gradual transitionadditionally provides a benefit of grading the reflectance between thetwo regions in a manner taught in a commonly assigned U.S. patentapplication Ser. No. 11/833,701, incorporated herein by reference in itsentirety. The gradual transition in reflectance or transmittance is notreadily noticed by an observer and a relatively large difference ofreflectance or transmittance between a display and another region canexist without being readily apparent to a casual observer. In contrast,if a discrete transition is present, the interface between the regionsbecomes noticeable even with very small changes in reflectance ortransmittance. Similarly, if the color changes gradually, the differencebetween two regions is harder to perceive. By way of example, in theembodiment 889 of FIG. 8(J), a graded chromium OREL coating 886 may bedeposited on a glass substrate 890 and positioned behind the surface VIof the embodiment 836 of FIG. 8(D). A gap 892 between the surface VI andthe Cr-layer is filled with the index-matching oil having a refractiveindex of 1.5. As shown, the chromium coating is absent on the portion ofthe glass 890 that overlaps with the display region of the assembly andtransitions from zero thickness to approximately 500 Å (in the opaqueregion) over the extent of about 1.5″. FIG. 14(B) shows a gradual,without discontinuities change in reflectance of the embodiment 889 ofFIG. 8(J) as a function of position, measured from the display regionthrough the transition region to the region of full opacity in 0.25 inchincrements. Table 8 shows the corresponding reflectance values (cap Y)and the reflected color (a* and b*). As can be seen from Table 8, thecolor variation is also smooth and the color difference between the twozones (the display region and the opaque region) is minimal. Preferably,the color difference between the two regions (the display region and theregion of full opacity) is less than 5, preferably less than 3, mostpreferably less than 1 units. The color difference ΔC* is defined usingthe following formula:

Color Difference=ΔC*=√{square root over ((a*−a*′)²+(b*−b*′)²)}{squareroot over ((a*−a*′)²+(b*−b*′)²)}

where (a*, b*) and (a*′,b*′) are the values describing color of lightreflected by the mirror system at two different positions across themirror.

TABLE 8 Position (inches) Cap Y a* b* 0 46.4 −2.0 −2.3 Display 0.25 46.3−2.1 −2.2 region 0.5 46.2 −2.0 −2.3 0.75 46.1 −2.0 −2.4 1 46.2 −2.0 −2.31.25 46.7 −2.1 −2.2 Opaque 1.5 48.7 −2.4 −1.6 region 1.75 52.2 −3.0 −0.72 56.1 −3.4 0.1 2.25 60.4 −3.7 0.8 2.5 65.0 −3.8 1.4 2.75 66.3 −3.8 1.5

The graded zone may generally consist of a single graded metal, alloy orcompound, or it may consist of multiple layers selected and designed toattain desired reflectance and transmittance in the opaque region, thedesired reflected color in the opaque region, and the transitionbehavior between the display and opaque regions. The transition regionmay be characterized by the rate of change of reflectance or color, orthe layers may be designed to minimize the color difference between thetwo zones with no undesired color behavior in the transition zone.

In some embodiments, light generated by the display of the embodimentsis polarized, for example, when a LCD is used with a mirror assembly. Inreference to the embodiments of FIG. 8(A) or 8(D), for example, theportion of the display-generated light 820 that traverses the componentsof the mirror assembly and reaches the viewer 115 is typically linearlypolarized at about 45 degrees to the vertical, which is represented inFIGS. 8(A,D) by y-axis. Such orientation of the LCD-generated light isdictated by a conventional structure of an LCD, which comprises acorrespondingly oriented linear polarizer through which the light passesupon being emitted. For normal indoor viewing of LCD displays, the angleof polarization of the emitted light does not directly affect theviewer's ability to see the displayed image. However, when an LCDdisplay is to be viewed outdoors or in a vehicle, where the ambientlight is sufficiently bright, the user may be wearing sunglasses. Theuse of sunglasses and, in particular, polarizing sunglasses, by thedriver of an automotive vehicle may become a criterion for design ofautomotive mirror assemblies that comprise displays.

Typically, polarizing sunglasses employ a linear polarizer to reduce theintensity of an apparent glare originating from reflection of ambientlight from various surfaces. The reflection of light is described bywell-known Fresnel equations that take into account a polarization stateof light. For example, polarizing sunglasses that utilize a polarizingfilter with a transmission axis oriented vertically (i.e., along they-axis as seen in FIG. 8(A), for example) reduce the intensity of thes-polarized (horizontal) component of ambient light thereby reducing theapparent glare from horizontal surfaces. Since the vector of linearpolarization angle of light emitted by most LCD displays isconventionally oriented at 45 degrees relative to the transmission axisof the typical polarizing sunglasses, the brightness of the LCD displayperceived by the user wearing such polarized sunglasses will be reducedby about 50%. For a driver of an automotive vehicle that observes thedisplay in the rearview mirror assembly the perceived reduction of thedisplay intensity may be undesirable.

In one embodiment, the light output of the display may be depolarized bya depolarizer such as a stretched polyester film, for example, or anyother suitable depolarizer. The use of a depolarizer is describedgenerally above and in detail in a commonly assigned U.S. PatentPublication 2008/0068520. As shown in FIG. 13(A), a depolarizer 1302 maybe placed between the display 639 and the transflective mirror assembly1304 (which may be, for example, the embodiment 800 of FIG. 8(A) or anyembodiment of the mirror system of the present invention).Depolarization of light 820 from the display prevents the polarizingsunglasses 1306 from interfering with the driver's ability to perceivethe display light. A similar depolarizing effect may be obtained, forexample, in an mirror structure embodiment 2020 of FIG. 20, by placing adepolarizer 2010 between the reflecting polarizer 824 (DBEF-Q) and theglass substrate 610 of the electrochromic element 840. As shown, theembodiment 2010 of FIG. 20 is similar to the embodiment 836 of FIG. 8(D)but it contains, in addition, the depolarizing layer 2010 comprisingstretched polyester such as Flexmark PM™ 200 or uncoated PP2500transparency film (available from 3M, Inc.) placed between thereflective polarizer 824 and the observer 115. As shown, a layer 2030 ofpressure sensitive adhesive (PSA) may be operationally connecting the RP824 and the depolarizer 2010. In another embodiment, the same effect maybe obtained by placing a depolarizer directly on the face of a mirrorassembly. In an embodiment similar to any of the embodiments of thecurrent invention, such as the embodiment of FIG. 8(D), for example, adepolarizer may be disposed on surface I of the glass plate 635. Inanother embodiment, the same effect may be obtained by using adepolarizing transparent layer such as plastic layer, in place one orboth of the lites of glass forming an EC-cell. For example, in oneembodiment, at least one of the plates 610 and 635 of FIG. 8(D) may bemade of a depolarizing plastic material. In another embodiment, the sameeffect may be obtained through the use of an optically anisotropic orbirefringent material placed in the electrochromic fluid of theEC-element (such as the element 614 in FIG. 8(D)). The degree ofpolarization can be defined as extinction value,(T_(high)−T_(low))/(T_(high)+T_(low)), where high and low represent theintensity values of light in the two polarization states having,respectively, high and low intensity. When light is highly polarized,the extinction value will be high. Table 9 below shows the transmittedand reflected polarization values for systems with and without opaquemetals present. Both transmission and reflection cases represent arelatively high extinction baseline for the system without the additionof a depolarizer. The samples used are described in Table 9 and twoexperimental samples of each configuration are shown. The high and lowpolarized intensity values are also listed. These values are used tocalculate an extinction percentage using the formula defined above. Lowextinction values equate to relatively equal intensities of the twopolarization states. The difference value listed in Table 9 representsthe percent change in extinction relative to the appropriate referencesample.

TABLE 9 Sample Description low high Extinction Difference TransmittanceUncoated 1.6 mm glass/8161 PSA/depolarizer/DBEF/¼ 18.4 60.5 53.36%35.97% wave TiO2-ITO bi-layer coating on 1.6 mm glass Uncoated 1.6 mmglass/8161 PSA/depolarizer/DBEF/¼ 20.3 58.8 48.67% 40.66% wave TiO2-ITObi-layer coating on 1.6 mm glass Uncoated 1.6 mm glass/depolarizer/3MPSA DBEF/¼ wave 22.5 58.8 44.65% 44.68% TiO2-ITO bi-layer coating on 1.6mm glass Uncoated 1.6 mm glass/depolarizer/3M PSA DBEF/¼ wave 23 54.440.57% 48.76% TiO2-ITO bi-layer coating on 1.6 mm glass Uncoated 1.6 mmglass/depolarizer/DBEF/¼ wave TiO2- 21.1 53.9 43.73% 45.60% ITO bi-layercoating on 1.6 mm glass Uncoated 1.6 mm glass/depolarizer/DBEF/¼ waveTiO2- 24.3 53.2 37.29% 52.04% ITO bi-layer coating on 1.6 mm glassUncoated 1.6 mm glass/DBEF/uncoated 1.6 mm glass 5.1 90.5 89.33% 0.00%Reflectance Uncoated 1.6 mm glass/8161 PSA/depolarizer/DBEF/ 59.4 84.317.33% 9.48% chrome coating on 1.6 mm glass Uncoated 1.6 mm glass/8161PSA/depolarizer/DBEF/ 60.1 83.9 16.53% 10.28% chrome coating on 1.6 mmglass Uncoated 1.6 mm glass/depolarizer/3M PSA DBEF/chrome 65.5 76.57.75% 19.06% coating on 1.6 mm glass Uncoated 1.6 mmglass/depolarizer/3M PSA DBEF/chrome 63 80 11.89% 14.92% coating on 1.6mm glass Uncoated 1.6 mm glass/depolarizer/DBEF/chrome coating 61.5 81.914.23% 12.58% on 1.6 mm glass Uncoated 1.6 mmglass/depolarizer/DBEF/chrome coating 65.1 80.3 10.45% 16.36% on 1.6 mmglass Uncoated 1.6 mm glass/DBEF/uncoated 1.6 mm glass 53.1 92 26.81%0.00%

The samples described in a “Reflectance” portion of Table 9 (the“reflectance samples”) show about a 40% to 50% improvement in theextinction. Visual examination of these samples with Polaroid sunglassesshowed a substantially decreased sensitivity to head tilt and,therefore, less changes due to head tilt in the reflected andtransmitted light. The term head tilt refers to rotation of thepolarization system of the polarizing sunglasses. The mirror systemcontaining such samples has lower initial extinction values than thesystem containing samples described in “Transmittance” portion of Table9 (the “transmittance samples”). This is due to the presence of a metallayer behind the reflective polarizer reflecting a substantialpercentage of the “low” polarization state. The presence of chrome layerin “reflectance samples” adds approximately 40% more light of the lowpolarization state relative to the high state. This gives the initialreference system without the depolarizer an extinction value of about26%, essentially comparable with or better than that of the system thatincludes a “transmission sample” and a depolarizer. The extinction valuecan be further reduced by substituting the chrome with a metal havinghigher reflectance. This, as noted above, will increase the reflectanceof the system and simultaneously reduce the extinction value by addingmore light in the “low” polarization state. This beneficialcharacteristic enables another possible embodiment—the benefits of adepolarizer can be obtained without a depolarizer in the area where thechrome, metal or other reflectance enhancement means is present and theadjustment of the LCD/reflective polarizer's polarization angle can bejudicially performed to more closely match the transmitted state of thePolaroid sunglasses (as discussed above). The reflected image in thearea of the display would be reduced in a commensurate amount whenviewed with Polaroid sunglasses but the image in the remainder of themirror would remain relatively high. A viewer not using Polaroidsunglasses would not be affected by this particular configuration.

In a related embodiment, the brightness of the display, perceived by thedriver wearing polarizing sunglasses, may be increased by rotating thevector of polarization of the display-generated light, upon light'spassing through the mirror assembly towards the driver, to make itco-linear with the transmission axis of the sunglasses. As shown in FIG.13(B), for example, such rotation may be achieved with the use of apolarization rotator 1308 appropriately disposed in front of thetransflective mirror assembly 1304 to reorient the polarization vectorof light 820′, emanating from the assembly 1304 towards the user 115,along the transmission axis of the sunglasses 1306. In a specificembodiment, the polarization rotator 1308 may comprise a half-wave plate(made of a birefringent film, for example) having its transmission axisalong the bi-sector of an angle formed by the transmission axis of thepolarizing sunglasses and the polarization vector of light 820′. As aresult, the polarization vector of light 820, initially oriented inxy-plane at 45 degrees with respect to the y-axis, will be aligned withthe x-axis, according to the well-known principle of operation of thehalf-waveplate.

In an alternative embodiment (not shown), it may be preferred to disposethe LCD as a whole (or, alternatively, only the polarizing components ofthe LCD) at a predetermined angle in an xy-plane within the rearviewmirror so as to produce light emission 820 that is initially polarizedalong the transmission axis of the sunglasses worn by the driver. Insuch alternative embodiments, light 820 emitted by the LCD 639 may bep-polarized (i.e., polarized along the x-axis). If, in addition, thereflecting polarizer (which may be a part of transflective mirrorassembly 1304 according to any of embodiments of the present invention)is oriented so as to maximize the transmission of the LCD light 820through the transflective assembly, the brightness of the LCD perceivedby the driver 115 through the sunglasses 1306 may be also optimized. Forexample, in reference to FIG. 15(A), a conventionally oriented LCD 639may emit light with luminance of 1,000 cd/m² and lenses of thepolarizing sunglasses 1306 may transmit 20% of p-polarized light and 0%of s-polarized light. Then, the transmission of unpolarized lightthrough polarizing sunglasses 1306 will be about 10%. Should adepolarizer 1302 be used between the LCD 639 and the transflectiveassembly 1504, the effective luminance of LCD light reaching the user115 through the sunglasses 1306 would be about 100 cd/m². In comparison,if the LCD system is oriented to provide p-polarized light output 820,the effective luminance perceived by the observer 115 through the samepolarizing lens 1306 increases to about 200 cd/m². At the same time, thebrightness of the ambient light reflected by such embodiment towards thedriver in sunglasses may be minimized, which worsens the performance ofthe mirror assembly as a reflector. The use of depolarizer 1302 with aconventionally oriented LCD 639, as shown in FIG. 15(A), may thereforebe preferred overall to rotating the LCD as described above.

In the following, additional embodiments of the invention are discussedand compared in reference to FIG. 3. In one embodiment, the composite312 was vacuum bagged, then placed into an autoclave for 1 hour at 90°C. at 100 psi. The resulting laminate 314 did not display any pattern ofdegradation and showed substantially no obvious extended distortions.FIG. 14 shows an image of a reference grid formed in reflection,according to the visual evaluation test, from another embodiment of thelaminate comprising a 1.6. mm thick glass substrate and a DBEF-Q film.The superstrate, preliminarily treated with Aquapel®, was released fromthe laminate according to the embodiment of the invention. This laminatewas prepared by vacuum bagging and autoclaving at about 90° C. and 200psi for about an hour and demonstrates quality adequate for automotiveuse. Generally, the temperature chosen for lamination processes in theabove implementations approximately corresponds well to the start of theglass transition onset temperature of the DBEF-Q polarizing film, asshown in FIG. 15. The glass transition temperature of the plastics is awell known physical characteristic of a plastic or multilayer plasticstructure and based on these experiments the lamination temperatureshould preferably be at or near the T_(g) in order to attain a laminatewith optical properties sufficient for automotive use. There exists aninterrelationship between the pressure, temperature, humidity, and timenecessary for a given APBF material to attain the desired opticalproperties. For instance, it may be possible to shorten the laminationtime if higher lamination pressure is applied at a slightly higherlamination temperature. We also discovered that the temperature forlamination of the reflective polarizer material may be controlledsomewhat independently from that of the substrate by using infraredheating at wavelengths that are transparent for the glass but absorbingby the reflective polarizer. In this manner the stress profiles in thematerials used for lamination may be controlled or modified, thereforefacilitating higher quality of the resulting laminate.

In contradistinction, and as a comparative example of a commercialproduct produced with a reflective polarizer having unacceptablereflective optical properties, a laminate-containing reflector (formedby a display of “Miravision” mirror-television set, manufactured andsold by Philips Corporation, model number 17MW9010/37, S/N1BZ1A0433816730, manufacture date August 2004) was also evaluated fordistortions. The inside frame dimensions of the sample are indicated ina diagram of FIG. 16. This commercial product included an opaquereflective area 1602 in the upper portion of the sample and a partiallyreflective/partially transmissive area 1604 in front of a display in thelower portion of the display, as indicated in the diagram. The mirror inthe lower portion obtains at least part of its reflectance by the use ofa reflective polarizer. The sample was examined using the visualevaluation test described above. The sample showed extended distortionsin the display region, particularly in the y-direction. Furthermore, asperceived visually, the waviness of the reflective laminate wasexacerbated if the viewer moved his head relative to the mirror. Thisworsening of the optical distortion with relative motion is aparticularly negative trait for automotive mirror applications, where areflected image must be equally well perceived at various angles. Thissample proved to be unacceptable for use in an automotive rearviewmirror, similarly to the commercial reflector described with referenceto FIG. 2. Specific results of evaluation of this sample withBYK-Gardner wave-scan dual device are provided in Table 10. As shown,the average of three short-wave and long-wave (SW and LW, respectively)readings were taken directionally in x- and y-direction, in thecorresponding regions labeled as X1 . . . X3 and Y1 . . . Y3 in FIG. 16.The values of SW in excess of 3, measured in the y-direction, areconsistent with the presence of the unacceptable waviness.Characterization of the region of the opaque mirror outside the displayarea demonstrates values that are substantially lower than those takenin the display region.

TABLE 10 LW SW X1 (avg) 0.5 0.5 X2 (avg) 1.1 0.5 X3 (avg) 0.7 0.5 Y1(avg) 0.2 3.6 Y2 (avg) 0.3 3.9 Y3 (avg) 0.2 3.5 XM (avg) 0.77 0.5 YM(avg) 0.24 3.7

In certain applications the laminate containing a reflective polarizeris exposed to relatively harsh environments. Automotive applications arean example of an environment that requires a component to pass stringentdurability tests (environmental durability tests) for the product to bequalified for use. The durability tests vary by automotive company butthere are a number of common tests a product is expected to pass. Thetests are designed to ensure that a product will function adequately forthe life of a vehicle. One of the tests is a so-called “hightemperature/high humidity” test, where the part or component is placedin a test chamber, e.g., at approximately 85° C. and 85% humidity. (Theprecise temperature, humidity and duration of the test can varydepending on the requirements of an automotive company.) Another test isa “high temperature storage” test where the component is kept at about105° C. for various lengths of time. (Four days or 96 hours is a commonduration of such test.) In other tests the component is kept at lowertemperature (85° C.) for up to 1,500 hours. Yet another test is a socalled “thermal shock” test, where the component repeatedly undergoesheating and cooling in cycles, e.g., between −40° C. and +85° C., with 1hour dwell, often with high humidity conditions. The hold time, ramptime, temperature extremes and number of cycles may vary depending onthe requirements imposed by an automotive company. Other tests have beendeveloped which combine the extreme conditions of the tests listed aboveto examine interaction effects. A failure in one or more of these testsmay be sufficient to prevent a given embodiment of a fabricatedcomponent or product from being commercialized. As a result ofenvironmental testing of various laminate embodiments of the inventionit was discovered that, generally: (i) embodiments fabricated at lowerlevels of pressure, such as 50 psi, have decreased durability; (ii) withincrease in lamination time, the durability of embodiments tends toincrease; (iii) an embodiment of the laminate of the invention havingboth a substrate and a superstrate (such as embodiment 314 of FIG. 3(C))has higher durability than the one with a superstrate released, whichdurability may be improved by post-lamination annealing.

Specifically, comparison of environmental durability of laminates havinga superstrate and those with a superstrate release was determined byfabricating and testing the samples made by laminating an APBF filmbetween the EC-element and the third lite of glass, according to thestructure of the embodiment 850 of FIG. 8(F) that additionally had agraded-thickness chromium layer deposited adjacent surface V. Prior tofabrication, the moisture content of the APBF film was maintained withinthe preferred limits as discussed above. The third lite of glass 826 waspre-treated with a release agent, as discussed in reference to FIG. 3,to allow for optional release of the superstrate 826. The laminatesamples under test were assembled along with control samples,vacuum-bagged, and autoclaved at 95° C. and 200 psi (gauge pressure) forabout 1 hour. All laminates were initially inspected visually fordefects and then exposed to the following environmental durabilitytests: 1) High Temperature Storage (105° C.), 2) High Temperature/HighHumidity Storage (85° C./85% RH), and 3) Thermal Shock (−40 to 85° C., 1hr dwell). The samples were inspected visually at variable timeintervals for various defects that are specific to individualenvironmental durability tests. Results of these tests are shown inTables 11, 12, and 13, respectively. As follows from these Tables, thelaminate embodiments that have a superstrate released (unprotectedsamples), even if initially acceptable through visual inspection, becameunacceptable for intended as a result of environmental durabilitytesting.

TABLE 11 High Temperature Storage test, 105° C. Sample Description 0 hrs24 hrs 48 hrs 72 hrs 96 hrs 168 hrs 336 hrs 504 hrs 672 hrs Control #1xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxx Control #2 xxxxxxxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxx Unprotected #1 xxxxxxxxxx xxx xxx xxx xxx xxx xx xx Unprotected #2 xxxxx xxxxx xxxx xxx xxxxxx xxx xx xx Legend: xxxxx = Excellent, no defects xxxx = Acceptable,small defects xxx = Unacceptable, bubbling, delamination, haze xx =Unacceptable, significant bubbling, delamination, haze x = Unacceptable,severe bubbling, delamination, haze Blank = Removed from testing

TABLE 12 High Temperature/High Humidity Storage test, - 85° C./85% RHSample Description 0 hrs 24 hrs 144 hrs 312 hrs 480 hrs 624 hrs 766 hrsControl #1 xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx Control #2 xxxxxxxxxx xxxxx xxxxx xxxxx xxxxx xxxxx Unprotected #1 xxxxx xx xx xx xx xxxx Legend: xxxxx = Excellent, no defects xxxx = Acceptable, smalldefects xxx = Unacceptable, bubbling, delamination, edge ingress xx =Unacceptable, significant bubbling, delamination, edge ingress x =Unacceptable, severe bubbling, delamination, edge ingress Blank =Removed from testing

TABLE 13 Thermal Shock test, −40 to 85° C., 1 hr dwell 75 150 213 433493 568 Sample Description 0 hrs cycles cycles cycles cycles cyclescycles Control #1 xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx Unprotected#1 xxxxx xx x X X x x Legend: xxxxx = Excellent, no defects xxxx =Acceptable, small defects xxx = Unacceptable, bubbling, delamination,edge ingress xx = Unacceptable, significant bubbling, delamination, edgeingress x = Unacceptable, severe bubbling, delamination, edge ingressBlank = Removed from testing

A similar set of experiments was directed to more completely understandthe effect of a post-lamination superstrate release on the durability ofa laminate of the invention. In this case, an APBF film was laminated,according to the embodiment 850 of FIG. 8(F), where glass lites 610 and826 were not coated with additional thin-film layers. Surface V of lite826 was pre-treated with a release agent to facilitate thepost-lamination release of the lite 826. This was accomplished byincorporating a release agent which allows for the removal of one liteof glass after lamination. Fabrication of both the samples under testand control samples was carried out under the conditions described inreference to Tables 11, 12, and 13. However, to improve adhesion of theAPBF to the uncoated glass plate 610, the samples were additionallyannealed post-lamination for 0, 30, or 60 minutes at 105°. The laminatedparts were initially inspected visually for defects and then submittedfor environmental durability testing: 1) High Temperature Storage (105°C.), 2) High Temperature/High Humidity Storage (85° C./85% RH), and 3)Thermal Shock (−40 to 85° C., 1 hr dwell). The parts were inspectedvisually at variable time intervals for various defects which arespecific to the individual environmental durability test. Results of theabove-mentioned tests, shown in Tables 14, 15, and 16, respectively,demonstrate that embodiments of the laminates the parts unprotected by ssuperstrate (i.e., having a superstrate 826 released) demonstrate poordurability in comparison with control samples. The unprotected sampleswere initially marginally acceptable or unacceptable by visualinspection but quickly all became unacceptable for use when subjected toenvironmental durability testing. The extra lite of glass incorporatedinto this embodiment significantly increases the environmentaldurability of the laminated devices.

TABLE 14 High Temperature Storage test, 105° C. Sample Description 0 hrs120 hrs 168 hrs 288 hrs 456 hrs 624 hrs 792 hrs 960 hrs Control xxxxxxxxxx xxxxx xxxxx xxxx xxxx xxxx Xxxx Control xxxxx xxxxx xxxxx xxxxxxxxxx xxxxx xxxx Xxxx 30 Minute Control xxxxx xxxxx xxxxx xxxxx xxxxxxxxxx xxxxx Xxxx 60 Minute Superstrate (3^(rd) lite) xx xx Xx xx x x x XRemoved, Control Superstrate (3^(rd) lite) xx xx Xx xx x x x x Removed,30 Minutes Superstrate (3^(rd) lite) xxxx xxx Xxx xxx xx xx xx xxRemoved, 60 Minutes Legend: xxxxx = Excellent, no defects xxxx =Acceptable, small defects xxx = Unacceptable, bubbling, delamination,haze xx = Unacceptable, significant bubbling, delamination, haze x =Unacceptable, severe bubbling, delamination, haze Blank = Removed fromtesting

TABLE 15 High Temperature/High Humidity Storage test, 85° C./85% RHSample Description 0 hrs 96 hrs 264 hrs 408 hrs 552 hrs 696 hrs 792 hrs960 hrs Control xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx Controlxxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx 30 Minutes Control xxxxxxxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx 60 Minutes Superstrate (3^(rd)lite) xx x Removed, Control Superstrate (3^(rd) lite) xx xx x Removed,30 Minutes Superstrate (3^(rd) lite) xxxx xx x Removed, 60 MinutesLegend: xxxxx = Excellent, no defects xxxx = Acceptable, small defectsxxx = Unacceptable, bubbling, delamination, edge ingress xx =Unacceptable, significant bubbling, delamination, edge ingress x =Unacceptable, severe bubbling, delamination, edge ingress Blank =Removed from testing

TABLE 16 Thermal Shock - −40 to 85° C., 1 hr dwell 135 205 280 355 430610 Sample Description 0 hrs cycles cycles cycles cycles cycles cyclesControl xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx Control xxxxx xxxxxxxxxx xxxxx xxxxx xxxxx xxxxx 30 Minutes Control xxxxx xxxxx xxxxx xxxxxxxxxx xxxxx xxxxx 60 Minutes Superstrate (3^(rd) lite) xx x Removed,Control Superstrate (3^(rd) lite) xxxx x Removed, 30 Minutes Superstrate(3^(rd) lite) xx x Removed, 60 Minutes Legend: xxxxx = Excellent, nodefects xxxx = Acceptable, small defects xxx = Unacceptable, bubbling,delamination, edge ingress xx = Unacceptable, significant bubbling,delamination, edge ingress x = Unacceptable, severe bubbling,delamination, edge ingress Blank = Removed from testing

The following series of samples were laminated via vacuum bagging andautoclaving (the latter occurring in pressurized gas or liquid) at 200psi and approximately 90° C. The different embodiments are contrastedusing thermal storage at 105° C. and 48 hours. These particular testconditions are not meant to be limiting and subtle differences betweenthe tests and laminates may be found with other tests or durations:

A laminate structured as [G/PSA/DBEF-Q/G], with PSA thickness of about 1mil, resulted in good image-forming quality and retained good qualityfollowing 48 hours of 105° C. storage.

A laminate structured as [G/DBEF-Q/G], where one of the glass plates hadbeen pretreated with a release agent (Aquapel™ available from PPGIndustries, Inc.) and then removed after the lamination procedureaccording to an embodiment of the invention, had good initial mirrorquality and retained good optical properties, i.e., image preservingreflector, following 48 hours of 105° C. storage.

The long-term stability of laminate-containing embodiments was monitoredby measuring the haze within the display region of the mirror structure.According to the standards of ASTM (American Society for Testing andMaterials), haze is defined as percentage of light that, duringtransmission through a sample, deviates by more than 2.5 degrees fromthe direction of the incoming beam of light. Haze measurements oflaminates structured according to the embodiment 850 of FIG. 8(F) wereaccomplished using a BYK Haze-gard Plus available from BYK-Gardner.Prior to fabrication of the embodiment 850, several APBF samples withprotective liners were subjected to 40° C. and 95% RH for 4 and 8 hours,respectively. Each of these samples, along with control samples of APBFstored under ambient conditions, was assembled with an EC-element,vacuum bagged, and autoclaved at 95° C. and 200 psi for about 1 hour toform mirror systems of the embodiment 850. The transmitted haze readingstaken after the fabrication of the embodiment and during the hightemperature storage test at 105° C. and at 24 hour intervals showed thatelevated pre-fabrication water content in APBF increases the haze levelsof the laminate up to 4 times. It was additionally showed thatpre-fabrication drying of the APBF samples under vacuum (e.g., at 40° C.and less than 50 torr pressure) removes the excess of water from theAPBFs, and results in the laminates that do not exhibit excessivetransmitted haze. Our study indicated that for long-term stability ofAPBF-containing laminates and mirror systems the APBF should preferablybe stored under relatively low humidity and levels of humidity should becontrolled during the lamination process. APBF-laminate-containingembodiments of the invention are characterized by transmitted hazelevels of less than 5%, more preferably less than 3%, and mostpreferably less than 1% as tested after high-temperature storage (e.g.,105° C. for 96 hours).

We found that fabrication, according to embodiments of the invention, ofAPBF-based laminates having high image-forming automotive opticalquality is consistent with but not necessarily limited to laminating anAPBF directly to a rigid optical substrate so as to provide asubstantially direct physical contact between at least one side of thefilm and a surface of a rigid optical substrate. Stated differently, weunexpectedly discovered that a laminate containing substantially no or aminimal amount of initially soft curable material such aspressure-sensitive adhesive (PSA) or other curable adhesive along atleast one lamination interface is very likely to satisfy the imagingquality requirements. We also found that simultaneous presence of someadhesive at both lamination interfaces (in the case of a laminatestructured according to FIG. 3(D), for example) the image-preservingreflecting properties of such laminate are more likely to be degraded.As a result, a rearview mirror assembly incorporating such a laminatewould be less likely to satisfy the existing optical quality standards.

We have also unexpectedly discovered that, for retaining a good mirrorquality after 48 hours of 105° C. storage, it may be beneficial toemploy embodiments of the APBF-containing laminates of the inventionwhere at least one side of the APBF is not be directly adhered to arigid substrate. That is, a laminate may be formed without a superstrateaccording to a general embodiment of FIG. 3(F) or, if an alternativeembodiment of FIG. 3(D) is used, the laminate may preferably include alayer of relatively pliable material, broadly defined asstress-relaxation means (such as flexible adhesive), between an APBF andonly one of the substrate and superstrate. In operation, a benefit ofusing a stress relaxation means stems from at least partial compensationof the differences in coefficients of thermal expansion (CTEs) betweenthe film and the substrate and/or superstrate. Generally, due to suchmismatch in CTEs, a laminate structured according to [G/RP/G] andexposed to elevated temperatures (e.g., during the storage test at 105°C.) acquires mechanical stresses resulting in visible degradation of theRP-film and substantial reduction of quality of the laminate. A stressrelaxation means, when present, may facilitate a relief of mechanicalstresses at elevated temperatures.

Table 17 shows the samples of data representing characterization of theextended distortions and the resulting optical properties of variousembodiments of the invention. Characterizations were conducted with theuse of wave-scan technique and by measuring the changes in optical powerof the surface-under-test as discussed above. As shown, samples 1through 3 represent inherent distortions observed in original reflectivepolarizer materials, and samples 4, 5, and 26 represent base-linedistortions for a glass substrate, an EC-element having ITO-coatings onsurfaces II and III, and an uncoated prism element, respectively. Asother samples demonstrate, these inherent distortions may be compensatedor reduced when the fabrication of a mirror system is carried outaccording to the process of the invention. In a case when thefabrication process is not adequately controlled, these inherentdistortions may be magnified and translated into the final product.Samples 6 and 24 represent the properties of an embodiment 2100structured according to [G/PSA/DBEF], see FIG. 21(A), which has a PSAlayer 2030 between the glass plate 826 and the APBF 824 and thesuperstrate released. Samples 6 and 24 were fabricated without and withautoclaving, respectively. The lamination process carried out undersubstantially omnidirectional pressure resulted in significantimprovement of the SW figures in the final laminate, but at the sametime reduced the LW values. Samples 7 and 20 were structured accordingto [G/PSA/DBEF/G], see embodiment 2110 of FIG. 21(B), which is alaminate having both the substrate and superstrate. Samples 7 and 20were fabricated with and without autoclaving, respectively. As can beseen from comparison of samples 6, 24 with samples 7, 20, the reductionof distortion characteristics of a laminate substantially relates notonly to the use of omnidirectional pressure during the fabrication ofthe laminate, but also to having the RP-layer of the laminate beingsupported by glass lites on both sides. This correlates with thefindings discussed above in reference to Tables 11 through 16. Samples 8and 19 correspond to the embodiment of FIG. 8(C), fabricated without andwith autoclaving, respectively. Both the wave-scan test and the opticalpower test demonstrate substantial reduction of extended distortions asa result of autoclaving procedure. Similar results have been obtainedfor samples 9 and 25, which corresponded to the embodiment 836 of FIG.8(D), fabricated without and with autoclaving, respectively. Each ofsamples 8, 19, 9, and 25 used DBEF-Q film as a reflective polarizer.Characterization of samples 11 and 13, each of which included prismaticelements, demonstrated substantial lack of extended distortion. Samples14, 16, and 17 represented the use of APBF different from the DBEF-Qproduct by 3M Inc. In particular, sample 14 was structured according tothe embodiment 850 of FIG. 8(F) and utilized the APF 35 film as areflective polarizer 824. Sample 15 represented a laminate-containingmirror structure depicted in an embodiment 2400 of FIG. 24. Theembodiment 2400 schematically illustrates a laminate of the invention,wherein the anisotropic film APF 35 used as a RP 824 is laminatedbetween the EC-element 840 and a third light of glass 610 having an ORELcoating deposited on surface V. In this embodiment, the OREL coatingincludes a 50 nm layer 2410 of Chromium and a 20 nm layer 2420 ofRuthenium. Sample 16 represented the embodiment 884 of FIG. 8(I) withAPF 50 as a reflective polarizer 824. Sample 17 also corresponded toFIG. 8(I), but utilized APF 50 as a reflective polarizer. DBEF-Q wasused as an RP in sample 21 structured according to the embodiment 884 of8(I). Samples 27 generally corresponded to the embodiment 884 of FIG.8(I). Sample 28 corresponded to an embodiment 2200 of FIG. 22 where, incomparison with the embodiment 884 of FIG. 8(I), the PSA layer 2030 hasbeen disposed between the RP 824 and glass plate 610. Both samplesdemonstrate substantial lack of extended distortions (characterized bySW and LW values) and excellent optical properties.

TABLE 17 # Sample Description SW LW Millidiopters 1 Original APF 35 film13.2 13.8 2 Original APF 50 film 17.9 5.2 3 Original DBEF-Q film 6.4 7.34 A glass substrate 0 0  81 . . . 141 5 An EC-element with ITO 0 0.2 156. . . 227 coatings on surfaces II and III 26 An uncoated glass prism 0.1. . . 0.2 0 6 Embodiment 2100 of FIG. 4.4 . . . 8.6 1.5 . . . 3.1 174 .. . 204 21(A), no autoclaving used 24 Embodiment 2100 of FIG. 2.7 4.7 .. . 4.9 21(A), with autoclaving 7 Embodiment 2110 of FIG. 5.7 21.9   227. . . 1,104 21(B), no autoclaving used. 20 Embodiment 2110 of FIG. 1.2 .. . 1.3 0.8 . . . 0.9 235 . . . 552 21(B), with autoclaving 8 Embodiment830 of FIG. 8(C),   2 . . . 3.7  6.1 . . . 11.1   432 . . . 2,100 noautoclaving used 19 Embodiment 830 of FIG. 8(C), 1.4 . . . 2.5 0.8 . . .0.9 208 . . . 257 with autoclaving 11 Embodiment 410 of FIG. 4(C)   1 .. . 1.5 0.6 . . . 0.9 13 Embodiment 2300 of FIG. 23,   0 . . . 2.2 0.1 .. . 1   with DBEF-Q as a reflective polarizer 14 Embodiment 850 of FIG.8(F), 4.8 . . . 5.1 0.4 295 . . . 476 with APF 35 as reflectivepolarizer 15 FIG. 2400 of FIG. 24, with APF 2.4 . . . 4.9 0.9 . . . 1.0327 . . . 375 35 as a reflective polarizer 16 Embodiment 884 of FIG.8(I), 0.1 . . . 0.2 0.1 285 . . . 361 with APF 35 as reflectivepolarizer 17 Embodiment 884 of FIG. 8(I), 8.7 . . . 9.8 0.6   527 . . .1,722 with APF 50 as reflective polarizer 21 Embodiment 884 of FIG.8(I), 0.6 . . . 1.2 0.5 . . . 2.4 250 . . . 592 with DBEF-Q asreflective polarizer 27 Embodiment 884 of FIG. 8(I), 0.7 . . . 1.2opaque 0.8 . . . 1.7 with DBEF-Q as reflective zone; 1.6 . . . 1.7opaque zone; polarizer transfl zone 0.4 . . . 0.6 transfl zone 28Embodiment 2200 of FIG. 22, 0.5 . . . 0.8 0.4 . . . 1.7 with DBEF-Q asreflective polarizer

Generally, embodiments of the invention may be configured to define aconvex element, an aspheric element, a planar element, a non-planarelement, an element having a wide FOV, or a combination of these variousconfigurations in different areas to define a mirror element withgenerally complex shape. In case of an electrochromic rearview mirrorassembly, the first surface of the first substrate may comprise ahydrophilic or hydrophobic coating to improve the operation. Theembodiments of the reflective elements may comprise an anti-scratchlayer on the exposed surfaces of at least one of the first and secondsubstrates. Examples of various reflective elements are described inU.S. Pat. Nos. 5,682,267, 5,689,370, 5,825,527, 5,940,201, 5,998,617,6,020,987, 6,037,471, 6,057,956, 6,062,920, 6,064,509, 6,111,684,6,166,848, 6,193,378, 6,195,194, 6,239,898, 6,246,507, 6,268,950,6,356,376, 6,441,943, and 6,512,624. The disclosure of each of thesepatents is incorporated herein in its entirety by reference.

Electrochromic mirror assemblies utilizing embodiments of the presentinvention contain an electrochromic medium that is preferably capable ofselectively attenuating light traveling therethrough and preferably hasat least one solution-phase electrochromic material and preferably atleast one additional electroactive material that may be solution-phase,surface-confined, or one that plates out onto a surface. However, thepresently preferred media are solution-phase redox electrochromics, suchas those disclosed in commonly assigned U.S. Pat. Nos. 4,902,108,5,128,799, 5,278,693, 5,280,380, 5,282,077, 5,294,376, 5,336,448,5,808,778 and 6,020,987. The entire disclosure of each of these patentsis incorporated herein in by reference. If a solution-phaseelectrochromic medium is utilized, it may be inserted into the chamberthrough a sealable fill port through well-known techniques, such asvacuum backfilling and the like. In addition, the disclosure of each ofU.S. Pat. Nos. 6,594,066, 6,407,847, 6,362,914, 6,353,493, 6,310,714 isincorporated herein by reference in its entirety.

Electrochromic medium preferably includes electrochromic anodic andcathodic materials that can be grouped into the following categories:

(i) Single layer: The electrochromic medium is a single layer ofmaterial that may include small inhomogeneous regions and includessolution-phase devices where a material is contained in solution in theionically conducting electrolyte and remains in solution in theelectrolyte when electrochemically oxidized or reduced. U.S. Pat. No.6,193,912 entitled “NEAR INFRARED-ABSORBING ELECTROCHROMIC COMPOUNDS ANDDEVICES COMPRISING SAME”; U.S. Pat. No. 6,188,505 entitled “COLORSTABILIZED ELECTROCHROMIC DEVICES”; U.S. Pat. No. 6,262,832 entitled“ANODIC ELECTROCHROMIC MATERIAL HAVING A SOLUBLIZING MOIETY”; U.S. Pat.No. 6,137,620 entitled “ELECTROCHROMIC MEDIA WITH CONCENTRATION ENHANCEDSTABILITY PROCESS FOR PREPARATION THEREOF AND USE IN ELECTROCHROMICDEVICE”; U.S. Pat. No. 6,195,192 entitled “ELECTROCHROMIC MATERIALS WITHENHANCED ULTRAVIOLET STABILITY”; U.S. Pat. No. 6,392,783 entitled“SUBSTITUTED METALLOCENES FOR USE AS AN ANODIC ELECTROCHROMIC MATERIALAND ELECTROCHROMIC MEDIA AND DEVICES COMPRISING SAME”; and U.S. Pat. No.6,249,369 entitled “COUPLED ELECTROCHROMIC COMPOUNDS WITH PHOTOSTABLEDICATION OXIDATION STATES” disclose anodic and cathodic materials thatmay be used in a single layer electrochromic medium, the entiredisclosures of which are incorporated herein by reference.Solution-phase electroactive materials may be contained in thecontinuous solution phase of a cross-linked polymer matrix in accordancewith the teachings of U.S. Pat. No. 5,928,572, entitled “IMPROVEDELECTROCHROMIC LAYER AND DEVICES COMPRISING SAME” or InternationalPatent Application No. PCT/US98/05570 entitled “ELECTROCHROMIC POLYMERICSOLID FILMS, MANUFACTURING ELECTROCHROMIC DEVICES USING SUCH SOLIDFILMS, AND PROCESSES FOR MAKING SUCH SOLID FILMS AND DEVICES,” theentire disclosures of which are incorporated herein by reference.

At least three electroactive materials, at least two of which areelectrochromic, can be combined to give a pre-selected color asdescribed in U.S. Pat. No. 6,020,987 entitled “ELECTROCHROMIC MEDIUMCAPABLE OF PRODUCING A PRE-SELECTED COLOR,” the entire disclosure ofwhich is incorporated herein by reference. This ability to select thecolor of the electrochromic medium is particularly advantageous whendesigning information displays with associated elements.

The anodic and cathodic materials can be combined or linked by abridging unit as described in International Application No.PCT/WO97/EP498 entitled “ELECTROCHROMIC SYSTEM,” the entire disclosureof which is incorporated herein by reference. It is also possible tolink anodic materials or cathodic materials by similar methods. Theconcepts described in these applications can further be combined toyield a variety of electrochromic materials that are linked.

Additionally, a single layer medium includes the medium where the anodicand cathodic materials can be incorporated into the polymer matrix asdescribed in International Application No. PCT/WO98/EP3862 entitled“ELECTROCHROMIC POLYMER SYSTEM,” U.S. Pat. No. 6,002,511, orInternational Patent Application No. PCT/US98/05570 entitled“ELECTROCHROMIC POLYMERIC SOLID FILMS, MANUFACTURING ELECTROCHROMICDEVICES USING SUCH SOLID FILMS, AND PROCESSES FOR MAKING SUCH SOLIDFILMS AND DEVICES,” the entire disclosures of which are incorporatedherein by reference.

Also included is a medium where one or more materials in the mediumundergoes a change in phase during the operation of the device, forexample, a deposition system where a material contained in solution inthe ionically conducting electrolyte which forms a layer, or partiallayer on the electronically conducting electrode when electrochemicallyoxidized or reduced.

(ii) Multilayer: The medium is made up in layers and includes at leastone material attached directly to an electronically conducting electrodeor confined in close proximity thereto which remains attached orconfined when electrochemically oxidized or reduced. Examples of thistype of electrochromic medium are the metal oxide films, such astungsten oxide, iridium oxide, nickel oxide, and vanadium oxide. Amedium, which contains one or more organic electrochromic layers, suchas polythiophene, polyaniline, or polypyrrole attached to the electrode,would also be considered a multilayer medium.

In addition, the electrochromic medium may also contain other materials,such as light absorbers, light stabilizers, thermal stabilizers,antioxidants, thickeners, or viscosity modifiers.

It may be desirable to incorporate a gel into the electrochromic deviceas disclosed in commonly assigned U.S. Pat. No. 5,940,201 entitled “ANELECTROCHROMIC MIRROR WITH TWO THIN GLASS ELEMENTS AND A GELLEDELECTROCHROMIC MEDIUM”. The entire disclosure of this U.S. patent isincorporated herein by reference.

In at least one embodiment of a rearview mirror assembly utilizing amirror element according to the present invention, the rearview mirrorassembly is provided with an electro-optic element having asubstantially transparent seal. Examples of EC-structures, substantiallytransparent seals and methods of forming substantially transparent sealsare provided in U.S. Pat. No. 5,790,298, the entire disclosure of whichis included herein by reference. U.S. Pat. Nos. 6,665,107, 6,714,334,6,963,439, 6,195,193, 6,157,480, 7,190,505, 7,414,770, and U.S. patentapplication Ser. No. 12/215,712 disclose additional subject matterrelated to seals and seal materials. The disclosure of each of thesesdocuments is incorporated herein by reference in its entirety.

In at least one embodiment, a mirror structure according to theinvention or a rearview mirror assembly utilizing such mirror structuremay include a spectral filter material and/or a bezel for protecting theassociated seal from damaging light rays and to provide an aestheticallypleasing appearance. Examples of various bezels are disclosed, e.g., inU.S. Pat. Nos. 5,448,397, 6,102,546, 6,195,194, 5,923,457, 6,238,898,6,170,956 and 6,471,362, the disclosure of each of which is incorporatedherein in its entirety by reference.

As discussed above, in at least one embodiment, an embodiment of theAPBF-containing laminate of the invention can be used in conjunctionwith a display such as an RCD, or another light source such as onegenerated polarized light, for example a laser source. Discussion ofvarious displays that can be used with embodiments of the invention isprovided, e.g., in U.S. Provisional Application No. 60/780,655 filed onMar. 9, 2006; U.S. Provisional Application No. 60/804,351 filed on Jun.9, 2006; U.S. Patent Application Publication Nos. 2008/0068520, U.S.Pat. No. 7,221,363; and U.S. patent application Ser. Nos. 11/179,798 and12/193,426. The entire disclosure of each of these applications isincorporated herein by reference. Generally, a light source can bedisposed as a stand-alone component separated from the mirror structureor it can be in physical contact with the mirror structure. Anembodiment of the laminate of the invention can also be beneficiallyused in applications utilizing rear-projection displays utilizing lasersources, e.g. a rear-projection display by Mitsubishi Corporationdescribed at www.lasertvnews.com/features.asp.

In at least one of embodiments, a mirror structure including anAPBF-based laminate of the invention may be configured in a rearviewmirror assembly that may include a glare light sensor or an ambientlight sensor, which are described in commonly assigned U.S. Pat. Nos.6,359,274 and 6,402,328. The disclosure of each of these patents isincorporated herein by reference in its entirety. The electrical outputsignal from either or both of these sensors may be used as inputs to acontroller on a circuit board of the assembly that controls theintensity of display backlighting. The details of various controlcircuits for use herewith are described in commonly assigned U.S. Pat.Nos. 5,956,012; 6,084,700; 6,222,177; 6,224,716; 6,247,819; 6,249,369;6,392,783; and 6,402,328, the disclosures of which are incorporated intheir entireties herein by reference. In addition or alternatively, therearview mirror assembly may include at least one additional device suchas, without limitation, an interior illumination assembly, a voiceactivated system, a trainable transceiver, a microphone, a compasssystem, a digital sound processing system, a highway toll boothinterface, a telemetry system, a moisture sensor, a global positioningsystem, a vehicle vision system, a wireless communication interface, acamera, a transflective reflector, a navigation system, a turn signal,and an adaptive cruise control system. These systems may be integrated,at least in part, in a common control with information displays and/ormay share components with the information displays. In addition, thestatus of these systems and/or the devices controlled thereby may bedisplayed on the associated information displays.

The embodiments of the invention described above are intended to bemerely exemplary; numerous variations and modifications will be apparentto those skilled in the art. For example, an embodiment of theAPBF-laminate-containing mirror system of the invention may bestructured according to the embodiments of a multi-zone reflector, asdisclosed in U.S. patent application Ser. No. 12/370,909 filed Feb. 13,2009, and contain various optical thin-film layers described thereinthat enhance the performance of the multi-zone reflector of theinvention. The reflectance-enhancing and opacifying layers may generallybe disposed in any pre-determined order adjacent at least one of thesurfaces of the structure to which the APBF is bonded, preferablyadjacent a surface located between the APBF and the light source. AnAPBF may substantially cover only a transflective zone of the mirrorstructure. Alternatively, the APBF may substantially cover the FOV ofthe multi-zone mirror. The transflective zone of the mirror structuremay contain additional transflective layers. A light source may be partof the laminate structure or a stand-alone component. All suchvariations and modifications are intended to be within the scope of thepresent invention as defined in any appended claims.

What is claimed is:
 1. A variable reflectance mirror system for use in arearview mirror, the variable mirror system having a front and a rearopposite thereto and comprising: at least one substrate comprising aplurality of surfaces; at least one reflective polarizer rearward of atleast one said substrate with respect to the front of the mirror system;wherein said at least one reflective polarizer comprises at least one ofan anisotropic film, a wire-grid, a linear polarizer, a circularpolarizer, and an optical retarder; wherein said at least one reflectivepolarizer is configured to transmit light having a first polarizationand reflect light having a second polarization; wherein the secondpolarization is different from the first polarization; a displayrearward of at least one said reflective polarizer with respect to thefront; wherein said display is configured to emit light having the firstpolarization that is transmitted by said reflective polarizer; an opaquereflectance-enhancement layer (OREL) rearward of said at least onereflective polarizer with respect to the front; and wherein said opaquereflectance-enhancement layer is opaque to light in a non-displayportion of the mirror system, such that light transmitted through saidat least one reflective polarizer is reflected in said non-displayportion.
 2. A mirror system according to claim 1, being a multi-zonereflector and having, in addition to an opaque zone in the non-displayportion of the mirror system, a transflective zone corresponding to adisplay portion of the mirror system.
 3. A mirror system according toclaim 2, wherein the opaque zone has a reflectance value exceeding 45percent measured in ambient light incident onto the first surface.
 4. Amirror system according to claim 2, wherein a color difference definedbetween the transflective and opaque zones in reflection of lightincident from a CIE standard D65 standard illuminant onto the firstsurface is less than 5 C* units of the CIELAB color system.
 5. A mirrorsystem according to claim 2, wherein a color difference defined betweenthe transflective and opaque zones in reflection of light incident froma CIE standard D65 standard illuminant onto the first surface is lessthan 3 C* units of the CIELAB color system.
 6. A mirror system accordingto claim 2, comprising a net quarter-wave thin-film stack reflectanceenhancement layer (REL) such as to increase a reflectance value of themirror system as measured from the front in at least the transflectivezone of the mirror system.
 7. A mirror system according to claim 6,wherein the reflectance value of the transflective zone exceeds 55percent.
 8. A mirror system according to claim 6, wherein thereflectance value of the transflective zone exceeds 60 percent.
 9. Amirror system according to claim 6, further comprising alternatinglayers of high and low refractive index materials adjacent to the netquarter-wave thin-films stack REL.
 10. A mirror system according toclaim 9, wherein the reflectance value of the opaque zone exceeds 50percent.
 11. A mirror system according to claim 9, wherein thereflectance value of the opaque zone exceeds 55 percent.
 12. A mirrorsystem according to claim 7, wherein the reflectance value of the opaquezone exceeds 60 percent.
 13. A mirror system according to claim 9,wherein the REL includes one or more of antimony trioxide, cadmiumsulfide, cerium oxide, tin oxide, zinc oxide, titanium dioxide orvarious titanium oxides, lanthanum oxide, lead chloride, praseodymiumoxide, scandium oxide, silicon, tantalum pentoxide, thallium chloride,thorium oxide, yttrium oxide, zinc sulfide, zirconium oxide, zinc tinoxide, silicon nitride, indium oxide, molybdenum oxide, tungsten oxide,vanadium oxide, barium titanate, halfnium oxide, niobium oxide, andstrontium titanate, and wherein a layer of low refractive index materialincludes one or more of aluminum fluoride, aluminum oxide, siliconoxide, silicon dioxide, calcium fluoride, cerium fluoride, lanthanumfluoride, lead fluoride, lithium fluoride, magnesium fluoride, magnesiumoxide, neodymium fluoride, sodium fluoride, thorium fluoride and aporous film with high density of voids.
 14. A mirror system according toclaim 1, wherein the OREL includes Cr, Al, Ag, Rh, Pd, Au, Ru, StainlessSteel, Pt, Ir, Mo, W, Ti, Cd, Co, Cu, Fe, Mg, Os, Sn, W, Zn and alloys,mixtures or combinations thereof.
 15. A mirror system according to claim1, wherein a ratio of intensity of light transmitted from the displaytowards the front to intensity of ambient light incident onto the firstsurface and reflected by the mirror system is greater than
 1. 16. Amirror system according to claim 1, wherein a ratio of intensity oflight transmitted from the display towards the front to intensity ofambient light incident onto the first surface and reflected by themirror system is greater than 1.25.
 17. A mirror system according toclaim 1 configured to be devoid of extended distortion.
 18. A mirrorsystem according to claim 17, wherein the extended distortion is opticaldistortion, caused by a distortion of a surface of the mirror system,and, when measured from the front, is characterized by one or more of:a) a curvature unit, of ONDULO phase-shifting deflectometry thatquantifies surface distortions, a modulus of which does not exceed 0.04,and b) an optical power value that quantifies surface distortions of themirror system, measured in reflection, which value does not exceed 1,000millidiopters; and c) SW and LW distortion metrics of a wave-scan dualscale, which metrics quantify surface distortions with frequenciescorresponding to ranges from about 0.1 mm to about 1.2 mm and from about1.2 to about 12 mm, respectively, and at least one of which is less than3.
 19. A mirror system according to claim 1, wherein the OREL comprisesa graded thickness in a region of transition between the transflectiveand opaque zones.
 20. A mirror system according to claim 1, furthercomprising at least one of an optical prism and an electro-optic medium.21. A mirror system according to claim 20, being an electro-optic mirrorsystem and comprising: a first transparent substrate including: a firstsurface corresponding to the front; a second surface opposite the firstsurface and carrying the first electrode; and a second substrate havinga third surface that carries a second electrode thereon and a fourthsurface opposite the third surface, the second substrate positioned in aspaced-apart and parallel relationship with respect to the first surfacewith the second and third surfaces facing each other to define a gaptherebetween, the electro-optical medium disposed in the gap such as tochange a transmittance value thereof in response to a voltagedifferential applied between the first and second electrodes.
 22. Amirror system according to claim 21, wherein the electro-optical mediumincludes electro-chromic medium.
 23. A mirror system according to claim1, further comprising a third transparent substrate at the rear of theat least one reflective polarizer with respect to the front.
 24. Amirror system according to claim 23, wherein the OREL is disposed on thethird substrate.
 25. A mirror system according to claim 1 having a totaltransmittance value in the range between about 25% to about 47%.
 26. Amirror system according to claim 1, having a polarized transmittancevalue in a range between about 25% and about 89.5%.
 27. A mirror systemaccording to claim 1, further comprising a depolarizing optical elementin front of the at least one reflective polarizer.
 28. A mirror systemaccording to claim 1, comprising a first reflective polarizer and asecond reflective polarizer an axis of polarization of which forms anangle with respect to an axis of polarization of the first reflectivepolarizer.
 29. A mirror system according to claim 28, wherein thereflectance value of the opaque zone exceeds 60 percent.
 30. A mirrorsystem according to claim 1, wherein the at least one reflectivepolarizer includes a dual brightness enhancement film.
 31. A mirrorsystem according to claim 1, configured to enable a ratio of a polarizedtransmittance value to an overall reflectance value characterizing themirror system to exceed
 1. 32. A variable reflectance mirror systemhaving a front, for use in a rearview mirror assembly, the mirror systemcomprising: at least one substrate having a plurality of surfaces; atleast one reflective polarizer rearward of at least one said substratewith respect to the front of the mirror system; wherein said at leastone reflective polarizer comprising at least one of an anisotropic film,a wiregrid, a linear polarizer, an elliptical polarizer, a circularpolarizer, and an optical retarder; a light source configured to emitlight of a first polarization towards the front of the mirror system andthat transmits through at least one said reflective polarizer; whereinsaid at least one reflective polarizer reflects light of a secondpolarization; wherein the second polarization is different than thefirst polarization; and a net quarter-wave thin-film stackreflectance-enhancing layer (REL) in front of said light source withrespect to the front of the mirror system; wherein said net quarter-wavethin-film stack reflectance-enhancing layer contributes to an increasein reflection of the mirror system.
 33. A mirror system according toclaim 32, further comprising at least one of an optical prism and anelectrochromic medium.
 34. A mirror system according to claim 33, beingan electrochromic mirror system and comprising: a first transparentsubstrate including: a first surface corresponding to the front; asecond surface opposite the first surface and carrying the firstelectrode; a second substrate having a third surface that carries asecond electrode thereon and a fourth surface opposite the thirdsurface, the second substrate positioned in a spaced-apart and parallelrelationship with respect to the first surface with the second and thirdsurfaces facing each other to define a gap therebetween, theelectro-optical medium disposed in the gap such as to change atransmittance value thereof in response to a voltage differentialapplied between the first and second electrodes.
 35. A mirror systemaccording to claim 32, wherein the surface of the mirror system thatcarries the REL is in front of the reflective polarizer as seen from thefront.
 36. A mirror system according to claim 32, wherein a ratio ofintensity of light transmitted from the light source towards the frontto intensity of ambient light incident onto the first surface andreflected by the mirror system is greater than
 1. 37. A mirror systemaccording to claim 32, wherein a ratio of intensity of light transmittedfrom the light source towards the front to intensity of ambient lightincident onto the first surface and reflected by the mirror system isgreater than 1.25.
 38. A mirror system according to claim 32, whereinthe reflectance value of the transflective zone exceeds 50 percent. 39.A mirror system according to claim 32, wherein the reflectance value ofthe transflective zone exceeds about 60 percent.
 40. A mirror systemaccording to claim 32, configured to be devoid of extended distortion.41. A mirror system according to claim 38, wherein the extendeddistortion is optical distortion, caused by a distortion of a surface ofthe mirror system, and, when measured from the front, is characterizedby at least one of: a) a curvature unit, of ONDULO phase-shiftingdeflectometry that quantifies surface distortions, a modulus of whichdoes not exceed 0.04; and b) an optical power value that quantifiessurface distortions of the mirror system, measured in reflection, whichvalue does not exceed 1,000 millidiopters; and c) SW and LW distortionmetrics of a wave-scan dual scale, which metrics quantify surfacedistortions with frequencies corresponding to ranges from about 0.1 mmto about 1.2 mm and from about 1.2 to about 12 mm, respectively, and atleast one of which is less than
 3. 42. A mirror system according toclaim 32, further comprising an auxiliary lite of glass at the rear ofthe at least one reflective polarizer with respect to the front.
 43. Amirror system according to claim 32, further comprising an opaquereflectance-enhancement layer (OREL) rearward of said at least onereflective polarizer with respect to the front; wherein said opaquereflectance-enhancement layer is opaque to light in a non-displayportion of the mirror system, such that light transmitted through the atleast one reflective polarizer is reflected in the non-display portion.44. A mirror system according to claim 43, wherein the OREL is disposedon an auxiliary lite of glass disposed at the rear of the at least onereflective polarizer with respect to the front the third substrate. 45.A mirror system according to claim 32, being a multi-zone reflector andincluding an opaque zone and a transflective zone.
 46. A mirror systemaccording to claim 45, wherein a color difference defined between thetransflective and opaque zones in reflection of light incident from aCIE standard D65 standard illuminant onto the first surface is less than5 C* units of the CIELAB color system.
 47. A mirror system according toclaim 46, wherein the at least one reflective polarizer includes a dualbrightness enhancement film.
 48. A variable reflectance mirror systemhaving a front, for use in a rearview mirror assembly, the mirror systemcomprising: a first substrate comprising a first electrode disposed on asurface thereof; a second substrate rearward of said first substratewith respect to the front of the mirror system, said second substratecomprising a second electrode disposed on a surface thereof; whereinsaid first substrate and said second substrate are in a spaced-apartrelationship to define a gap therebetween; an electrochromic mediumdeployed in said gap; wherein a transmittance of said electrochromicmedium changes in response to a potential difference applied thereto; atleast one light source rearward of said second substrate, said lightsource adapted to emit light of a first polarization towards the frontof the mirror system; at least one reflective polarizer comprising adual brightness enhancement film and positioned between said secondsubstrate and said light source; wherein light of the first polarizationtransmits through at least one said reflective polarizer; wherein lightof a second polarization is reflected by at least one said reflectivepolarizer; wherein said second polarization is orthogonal to said firstpolarization; an opaque reflectance-enhancement layer disposed rearwardof said at least one reflective polarizer with respect to the front ofthe mirror system; wherein said opaque reflectance-enhancement layer isconfigured to reflect light that transmits through at least one saidreflective polarizer; wherein said opaque reflectance-enhancement layerdefines a transmissive zone and an opaque zone of the mirror system; anda net quarter-wave thin-film stack reflectance-enhancing layer in frontof the light source with respect to the front of the mirror system;wherein said net quarter-wave thin-film stack reflectance-enhancinglayer contributes to an increase in reflection of the mirror system.